Hazelnut Gateau with Praliné Buttercream and Fleur de Sel Brittle

Hazelnut gateau by Carol Walter was this month Daring Bakers’ challenge. I have to admit I changed it quite a bit preserving the whole idea in general. I used a different method for making the nut génoise – the one that never failed me before. For a soaking syrup I went with Frangelico liqueur. I didn’t make a Swiss buttercream but made a crème anglaise-based one. First, because I like it better, and second – I’ve recently made the Swiss buttercream to fill my Opera. As for chocolate glaze, I covered the cake with Alice Medrich’s glaze designed for the cakes being refrigerated. It does really stay beautiful even after prolong refrigeration time. I decorated the cake with crushed thin, and delicate hazelnut fleur de sel brittle. I wish we had more freedom in choosing the way to decorate the cake (the buttercream piping had to be present). Personally, I don’t like the idea of piping the buttercream over the chocolate glaze. Not that I don’t like the buttercream, I just think it’s too much of a good thing. That’s why there’s no elaborate buttercream design on the top of my cake. Overall, the cake was delicious. And I do see myself making it (or some variation of) again, somewhere in the autumn or winter. It is not a summer time treat. I’d rather stick to the fresh fruit and crème chantilly.

Hazelnut Gateau with Praliné Buttercream and Fleur de Sel Brittle

Make 10-inch cake, enough for a large crowd

For the hazelnut génoise:

  • 7 large eggs, at room temperature
  • 2 large egg yolks, at room temperature
  • 135 g (4 ¾ oz); 2/3 cup fine granulated sugar
  • 125 g (3 ½ oz); ¾ cup+2tbsp all-purpose flour
  • 20 g (3/4 oz); 2 tbsp potato cornstarch
  • 200 g (7 oz); 1 ½ cups hazelnut-and-sugar powder (see below)
  • 3 tbsp unsalted butter
  • 1 tsp pure vanilla extract

    Hazelnut-and-sugar powder:
  • 4 oz blanched hazelnuts
  • 4 oz confectioners’ sugar

Combine the nuts with half the confectioners’ sugar in the food processor. Process the nuts and sugar, stopping to scrape down the sides of the bowl and break up any caking as needed, until the nuts are finely ground, but not so long that the mixture becomes oily.

Sift through a medium sieve (1.5-2 mm mesh). Return the nuts that didn’t pass through the sieve to the food processor with the remaining confectioners’ sugar and process until the nuts been reduced to a fine powder.

Transfer the nut-and-sugar powder to a bowl, break up any caking with your fingertips, and mix thoroughly.

Covered airtight, the mixture can be stored up to a month at room temperature.

For the soaking syrup:

  • 1/2 cup heavy syrup (see below)
  • 1/2 cup Frangelico liqueur

Heavy syrup:

  • 1/2 cup (100 g) granulated sugar
  • 1/4 cup water

Combine the sugar and water in the small saucepan and bring to a boil, stirring occasionally to dissolve all the sugar. Cover and allow the syrup to cool.

Covered airtight, the syrup can be stored for up to several months at room temperature.

For the filling:

  • 1 recipe of praliné buttercream
  • ¾ cup whipping cream, chilled

For the praliné buttercream:

  • ½ cup whole milk
  • 1 cup fine granulated sugar
  • 6 large egg yolks, at room temperature
  • 1 tsp pure vanilla extract
  • 400 g (3 ½ sticks) unsalted butter, at room temperature
  • 2/3 cup praliné

For the praliné:

(it makes more than you will need for this recipe but the praliné can be kept up to 3 months in the refrigerator)

  • 200 g (7 oz) blanched toasted hazelnuts
  • 100 g (3 ½ oz); ½ cup fine granulated sugar
  • 100 g (3 ½ oz); 1 2/3 cups confectioners’ sugar

For the chocolate glaze:

  • 8 oz bittersweet or semisweet chocolate, finely chopped
  • 12 tbsp (1 ½ sticks) unsalted butter
  • 1 tbsp light corn syrup
  • 5 tsp water

For the fleur de sel hazelnut brittle:

  • 1 cup sugar
  • 1/3 cup water
  • 1/8 tsp cream of tartar
  • ½ cup finely ground toasted hazelnuts
  • ½ tsp fleur de sel

Make the hazelnut génoise:

Center an oven rack and preheat the oven to 375F.

Butter and dust with flour a 10-inch round cake pan. Line the bottom of the pan with parchment paper circle, butter the parchment.

In a small saucepan, or in a microwave-safe cup in a microwave, heat the butter, without stirring, until it is melted and hot. Spoon off and discard the foam from the surface. Transfer 2 tbsp of the clear yellow butter to a medium heatproof bowl leaving the watery liquid behind. Add the vanilla to the bowl and set aside.

Sift the flour and potato flour together three times; then mix in the hazelnut-and-sugar powder. Set aside.

In a bowl of your electric mixer, using a whisk, combine the eggs and sugar thoroughly. Place the bowl in a wide skillet of barely simmering water. Whisking constantly, heat the eggs to lukewarm (about 105F). Remove the bowl from the pan; leave the skillet on the stove but turn off the heat. With an electric mixer, beat the egg mixture at high speed until it has cooled, tripled in volume, and resembles softly whipped cream, about 5 minutes in a heavy-duty mixer or longer with a less powerful mixer.

Meanwhile, set the bowl of butter and vanilla in the skillet of hot water, with the burner off, to keep it warm.

Dust about one-third of the flour and nut mixture over the whipped eggs. Use a rubber spatula to fold in the mixture – quickly but gently – until combined. Fold in half the remaining flour and nuts, then fold in the rest. Remove the warm butter mixture from the skillet. Scoop about 1 cup of the batter into the bowl with the butter and fold together until completely combined. Use the large rubber spatula to fold the butter mixture completely into the remaining batter. Turn the batter into the prepared pan and tilt to level. Place the cake pan onto a baking sheet and slide it into the oven.

Bake until the cake beginning to shrink slightly around the edges and the top springs back when pressed with your finger, about 40-45 minutes. Cool the cake in the pan on a rack for 5 minutes. To unmold, run a small knife or spatula around the inner edges of the pan. Invert it onto a rack and remove the parchment liner. Turn the cake right side up. Cool completely on the rack. The génoise can be wrapped and refrigerated for up to 2 days, or frozen for up to 3 months.

Make the soaking syrup:

Combine ½ cup of the heavy syrup with ½ cup of the liqueur. Cover, set aside until ready to use.

Make the praliné:

Line a large baking pan or a cookie sheet with parchment, foil, or a silicone mat. Set aside.

In a heavy small saucepan over moderate heat, stir together the granulated sugar and water. Cook, stirring occasionally, until the sugar dissolves, then raise the heat to moderately high and boil without stirring, occasionally brushing down sides of the pan with a wet pastry brush, until the syrup turns golden caramel in color. Stir the hazelnuts into the caramel syrup. Continue heating, stirring constantly with the spatula, until the nuts and caramel are combined. Pour the nut-and-caramel mixture onto the prepared baking pan and let cool completely.

Break the hazelnut brittle into pieces and combine it with the confectioners’ sugar in the bowl of the food processor. Process to pulverize the brittle. Continue processing until the brittle is reduced to a smooth, creamy paste, with just a slight grittiness. This will take some time and the praliné will become hot.

Transfer the praliné to a bowl and let it cool to room temperature.

Covered airtight, the praliné will keep for up to 3 months in the refrigerator. If some oil separates on the top of the praliné, stir it back before using.

Bring to room temperature before incorporating into the buttercream.

Make the praliné buttercream:

Combine the milk and half of the sugar in a heavy saucepan and bring to a simmer.

Right before the cream is ready, in a medium bowl whisk the egg yolks and remaining sugar together until smooth and lemon-colored. Gradually, in a very thin stream, add the hot milk, whisking constantly. Pour this mixture back into the saucepan and return to the stove. Stir constantly with a wooden spoon over medium heat until the custard thickens and coats the back of the spoon. Immediately strain the custard through the fine sieve into the bowl of the stand mixer. Add the vanilla extract. Beat the custard with the wire whip at medium speed until it is light and cool.

Replace the wire whip with the paddle attachment. Gradually, 2 tbsp at a time, beat in the softened butter at medium speed. When all of the butter has been incorporated, beat the buttercream vigorously for a minute on high speed to make it as light as possible.

Measure 2/3 cup of the praliné (room temperature) into a medium bowl. Using a wooden spoon, gradually beat in about 1 cup of the buttercream. Make sure the mixture is smooth. Then beat the flavored portion back into the remaining unflavored buttercream.

Covered airtight, the buttercream can be kept for up to a week in the refrigerator. Before using, let the buttercream soften at room temperature. Then beat it with the flat beater of the mixer to make it smooth, spreadable, and light.

The buttercream can be frozen for up to 3 months. Defrost overnight in the refrigerator.

Fill the cake:

Cut the cake horizontally into 3 even layers. Set aside.

Whip ¾ cup of the whipping cream until soft peaks form, set aside.

Place one layer of the génoise, cut side up, onto a cardboard circle. Brush about ¼ cup of the soaking syrup over the cake. Spread 1 ½ cups of the praliné buttercream over the cake surface. Spread half of the whipped cream over the buttercream leaving ¼-inch bare border around the edges. Moisten one of the sides of the middle génoise layer with ¼-cup of the soaking syrup, place this layer (moistened side down) over the first one. Brush the top of the middle layer with more syrup. Spread another 1 ½ cups of the buttercream over it; then spread the rest of the whipped cream. Moisten the cut side of the final génoise layer with the soaking syrup and invert it onto the cake. Press gently. Lightly moisten the top of the cake. Refrigerate for 30 minutes.

Use the rest of the buttercream to crumb-coat the top and the sides of the cake. If you wish, set a little bit of the buttercream aside for a decorative piping. Refrigerate the cake for at least 2 hours, better – overnight – before glazing.

Make the fleur de sel brittle:

Preheat the oven to 350F.

Line a large baking pan or a cookie sheet with parchment, foil, or a silicone mat. Set aside.

In a heavy small saucepan over moderate heat, stir together the sugar, water, and the cream of tartar. Cook, stirring occasionally, until the sugar dissolves, then raise the heat to moderately high and boil without stirring, occasionally brushing down sides of the pan with a wet pastry brush, until the syrup turns golden caramel in color. Pour the caramel onto the prepared baking pan and let cool completely.

Brake the caramel into 1-inch pieces and grind in a food processor to the consistency of granular sugar. Stir in the ground nuts.

Reline the baking sheet with parchment paper, foil, or a silicone mat. Spread the caramel mixture very thinly over the entire baking sheet (you might need to do it in two batches – the caramel layer has to be thin). Place the sheet in the oven to melt the caramel, for about 4-6 minutes. Remove from the oven. Immediately, sprinkle with the Fleur de Sel.

Once cool, chop the brittle finely (or not so finely – according to your preference). Do not use a food processor, or you will end up with what you started from.

Store the brittle in a cool dry place, for 2 weeks.

It’s not recommended to make the brittle when the weather is very humid.

Make the chocolate glaze, finish the assembly:


For the glaze, place all the ingredients in a small heatproof bowl set in a wide skillet of barely simmering water and stir frequently until the chocolate is almost completely melted; do not overheat. Remove the glaze from the water bath and set aside to finish melting, stirring once or twice until perfectly smooth. If necessary, before using, cool the glaze to 88-90 F. It will be optimally shiny if you pour it at that temperature. Place a sheet of parchment paper or foil under the rack with the cake and pour the glaze over the top of the cake. Any excess glaze may be refrigerated for up to a week or frozen.

Before the glaze has completely set press the chopped hazelnut brittle onto the sides of the cake. Sprinkle over the top as well (if you wish).

The leftover of the buttercream can be used for a decorative piping. The cake can be made several days in advance. But the brittle can’t keep that long – it will melt in the fridge. Choose another decoration if you need to assemble the cake well before serving.