Almond-Crunch Ice Cream Cake

Cake:

Preheat oven to 300 degrees with rack in center. Spread whole almonds in a single layer on a rimmed baking sheet; bake until golden, about 12 to 15 minutes. Transfer sheet to a wire rack; let cool completely.

Pulse whole almonds and cake flour in a food processor until finely ground, about 30 seconds.

Butter two 7-inch round cake pans. Line pans with parchment; butter parchment.

In the bowl of a mixer fitted with the whisk attachment, beat together egg whites and salt on medium speed until soft peaks form. Increase speed to high and gradually add 1/2 cup sugar, beating until stiff and glossy, about 4 minutes. Transfer to a bowl.

Clean mixer bowl and return to mixer fitted with the whisk attachment; beat together egg yolks and vanilla. With mixer on high speed, gradually add remaining 1/2 cup sugar, beating until pale and thick, about 5 minutes.

Fold egg-white mixture into egg-yolk mixture. In three additions, fold in almond mixture. Divide batter evenly between prepared pans, smoothing tops with an offset spatula.

Bake until a tester inserted in centers comes out clean, 18 to 20 minutes. Transfer pans to a wire rack; let cool completely. Turn out cakes and wrap in plastic until ready to use.

Almond Crunch:

Increase oven temperature to 325 degrees. In a medium bowl, toss together sliced almonds, granulated sugar, and 2 tablespoons water. Spread almond mixture evenly on a parchment-lined baking sheet. Bake until golden, about 25 minutes. Transfer sheet to a wire rack; let cool completely.

Assembly:

Bring granulated sugar and 1/3 cup water to a boil in a small saucepan over medium heat, stirring occasionally. When sugar has dissolved, remove from heat; add amaretto, if using, and almond extract. Let cool completely.

Using a serrated knife, split each cake horizontally into two equal layers.

Cut three 24-by-6-inch strips of parchment. Place strips on top of one another and use to line the sides of a 7-inch springform pan. Generously brush tops of cake layers with syrup. Place a cake layer in prepared pan.

In the chilled bowl of a mixer fitted with the paddle attachment, beat ice cream on medium-low speed until spreadable, about 2 minutes. Spread about 2 cups ice cream over first cake layer. Crumble 1/2 cup almond crunch over ice cream. Top with a second cake layer; transfer to freezer until firm, about 20 minutes. Repeat, spreading 2 cups ice cream and 1/2 cup almond crunch between each layer. Finish with a cake layer. Freeze 1 hour.

Just before serving, whisk cream and confectioners' sugar to medium peaks in a chilled bowl. Remove cake from freezer and release sides of pan. Transfer cake to a serving platter. Tuck parchment strips under perimeter of cake. Frost top and sides of cake with whipped cream; remove parchment strips. Garnish top with remaining almond crunch; serve immediately.