HAZELNUT GATEAU WITH COFFEE BUTTERCREAM

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Makes 10 servings

This classic cake, with toasty nut flavor in every bite, is just the sweet you might have at a French café with an afternoon coffee. It is made in the time-honored French manner: spongy génoise cake layers, soaked with liqueur-spiked syrup, frosted with rich buttercream. This buttercream, made with a base of egg whites, is one of the easiest and best around.

HAZELNUT GENOISE

  • 4 tablespoons (½ stick) unsalted butter
  • 1 teaspoon vanilla extract
  • 1 cup cake flour (not self-rising)
  • ¹/3 cup (1½ ounces) toasted, skinned, and coarsely chopped hazelnuts (see Note)
  • ½ teaspoon baking powder
  • ¼ teaspoon salt
  • 1 cup of sugar
  • 6 large eggs

FRANGELICO SYRUP

  • ²/3 cup sugar
  • ¹/3 cup hazelnut liqueur, such as Frangelico, or use hazelnut syrup for beverages

COFFEE BUTTERCREAM

  • 4 large egg whites
  • 1 cup of sugar
  • 1 pound unsalted butter, at cool room temperature
  • 3 tablespoons cold brewed espresso or
  • 4 teaspoons instant espresso powder dissolved in 3 tablespoons boiling water and
  • cooled
  • 1 cup (4 ounces) toasted and skinned hazelnuts (see Note)
  • 10 chocolate-covered espresso beans
  1. Position a rack in the center of the oven and preheat to 350°F. Line the bottom of a 9-inch springform pan with a round of parchment or wax paper. Do not butter or flour the pan.
  2. Melt the butter in a small, heavy-bottomed saucepan over medium heat, and let boil until the milk solids in the bottom of the pan turn light brown, 2 to 3 minutes. Remove from the heat and let stand for 1 minute. Skim the foam from the top of the butter. Carefully pour the browned butter into a medium bowl, leaving the browned milk solids behind in the saucepan. Add the vanilla.
  3. Process the flour, hazelnuts, baking powder, and salt together in a food processor fitted with the metal chopping blade until the nuts are ground into a powder, about 30 seconds. Set aside.
  4. Bring a medium saucepan with 1 inch of water to a brisk simmer over high heat. Reduce the heat to medium-low to maintain the simmer. Whisk the sugar and eggs together in the bowl of a heavy-duty standing mixer. Place over the water (the bowl should not touch the water) and whisk constantly until the sugar is dissolved and the egg mixture is hot (dip in your finger), about 2 minutes. Attach the bowl to the mixer and fit with the whisk attachment. Beat on high speed until the mixture is very pale and fluffy and has tripled in volume, about 4 minutes. (Another test: Stop the mixer and lift the whisk attachment. The mixture should form a thick ribbon that falls back on itself and stays on the surface for a few seconds before sinking.
    Professional bakers call this “making the ribbon.”) You can use a large heatproof bowl and a hand mixer to prepare the egg mixture but allow at least 5 minutes of beating.
  5. Remove the bowl from the mixer. In thirds, sprinkle the flour mixture over the egg mixture and fold it in with a large balloon whisk or a rubber spatula. Transfer about one-fourth of the batter to the butter-vanilla mixture and whisk together to combine. Return this mixture to the batter and fold it in. Pour into the pan and smooth the top.
  6. Bake until the top of the cake springs back when lightly pressed in the center with your fingers, about 35 minutes. Let cool in the pan on a wire cake rack for 10 minutes. Run a sharp knife around the inside of the pan to release the cake. Invert the cake onto the rack and remove the pan bottom and parchment. Turn right side up and let cool completely.
  7. To make the syrup, combine the sugar and ¾ cup water in a medium saucepan. Bring to a boil over medium heat, stirring to dissolve the sugar. Stop stirring and boil for 1 minute. Remove from the heat and let cool. Stir in the liqueur.
  8. To make the buttercream, bring a medium saucepan with 1 inch of water to a brisk simmer over high heat. Reduce the heat to medium-low to maintain the simmer. Combine the egg whites and sugar in a very clean bowl of a heavy-duty standing mixer. Place over the water (the bowl should not touch the water) and whisk constantly until the sugar is dissolved and the egg mixture is opaque white and hot (dip in your finger), about 2 minutes. Attach the bowl to the mixer and fit with the whisk attachment. Beat on high speed until stiff, shiny peaks form and the meringue is cool, about 6 minutes. (You can use a large heatproof bowl and a hand mixer to prepare the meringue. After heating the egg whites mixture, place the bowl on a wire cake rack to allow better air circulation to cool the mixture, and allow at least 8 minutes of beating.)
  9. One tablespoon at a time beat in the butter and continue beating until the buttercream is smooth and fluffy. Beat in the espresso.
  10. To assemble the cake, using a long serrated knife, cut the cake in half horizontally. Place the top layer (with the “skin”), cut side up, on a 9-inch cardboard cake round. Brush half of the syrup over the cake layer. Spread with about ½ cup of the buttercream. Top with the remaining cake layer, cut side down. Brush with the remaining syrup. Spread the top, then the sides, with a thin layer of buttercream. Refrigerate the cake until the buttercream is set, about 10 minutes.
  11. Transfer about ¾ cup of the buttercream to a pastry bag fitted with a
    ½-inch star tip, such as Ateco #825. Spread the top and then the sides of the cake with the remaining buttercream. Pipe 10 equally spaced rosettes around the top perimeter of the cake. Press handfuls of the chopped hazelnuts around the sides and over the top of the cake. Place an espresso bean in each rosette. Place the cake on a serving platter. (The cake can be made up to 1 day ahead, covered with a cake dome and stored at room temperature.) Slice and serve.

NOTE: To toast hazelnuts, spread the nuts on a rimmed baking sheet. Bake in a preheated 350°F oven until the skins are cracked and the nut flesh is golden brown, 12 to 15 minutes. Wrap the nuts in a clean kitchen towel and let stand until cool enough to handle. Using the towel, rub the skins off the nuts. Don’t worry about removing every last shred of skin.

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