Twelve Layer Mocha Cake

Preheat oven to 350 F with rack in middle. Butter 1 sheet pan and line bottom with parchment paper, then butter parchment. Dust with flour, knocking out excess.

Whisk together yolks, milk, vanilla, and 1/2 cup sugar in a large bowl until combined well, then whisk in flour and salt until smooth. (Batter will be thick).

Beat whites with an electric mixer until they just hold soft peaks. Beat in remaining 1/4 cup sugar, 1 tbsp at a time, and beat until whites just holds stiff peaks.

Fold one third of whites into batter to lighten, and then fold in remainder gently but thoroughly.

Spread batter evenly in pan and rap against counter to release any air bubbles. Bake until cake is dry to the touch and pale golden, 10 to 11 minutes. (Leave oven on). Cool completely in pan on a rack.

Halve cake crosswise, cutting through parchment, to form 2 (10-by 7 1/2 inch) layers.

Prepare soufflé layers wile cake bakes:

Line second sheet pan with parchment paper, melt chocolate with water, then cool to lukewarm.

Beat yolks, salt and 1/4-cup sugar in a large bowl with an electric mixer at high speed until thick and pale, about 5 minutes with a stand mixer. Fold in melted chocolate.

Beat whites with cleaned beaters until they hold soft peaks. Beat in remaining 1/4 cup sugar, 1 tbsp at a time, and beat until white just hold stiff peaks, about 5 minutes.

Fold one third of whites onto chocolate mixture to lighten, then fold in remainder gently but thoroughly. Spread batter evenly in lined sheet pan.

Bake soufflé layers:

Bake until puffed and a wooden pick inserted into center come out with a few crumbs adhering, 25 to 30 minutes. Transfer pan to a rack, then cover top of soufflé with 2 layers of damp paper towels. Let stand 5 minutes. Remove towels and cool soufflé completely in pan (soufflé will deflate as it cools). Sift cocoa over soufflé, and then loosen edges with a sharp knife.

Halve soufflé crosswise, cutting through parchment, to form 2 (10-by 7 1/2-inch) layers.

Make meringue layers:

Toast hazelnut, then cool wrapped in a kitchen towel, and rub off any loose skins.

Reduce oven to 250 F. finely chop nuts.

Beat whites with salt and cream of tartar using electric mixer until they just hold soft peaks. Beat in sugar, 1 tbsp at a time, and beat until meringue is stiff but still glossy.

Line bottom of third sheet pan with parchment. Put small dabs of meringue under corners of parchment to secure to baking sheet.

Fold nuts into meringue and spread evenly in pan. Bake until set and pale golden, 25 to 30 minutes.

Halve meringue crosswise, cutting through parchment, to form 2 (10-by 7 1/2 inch) layers. Return to oven and bake until crisp, 45 minutes to 1 hour more. Cool in pan, then peel of parchment.

Make syrup and assemble cake:

Bring water, sugar and espresso powder to a boil, stirring until sugar has dissolved. Cool.

Loosen edges of 1 cake layer with a knife and invert onto a flat patter. Carefully peel parchment from cake and brush with some of syrup. Spread with 1 1/4 cups mocha buttercream.

Top with 1 meringue layer and spread with 1 1/4 cups coffee buttercream.

Carefully invert 1 soufflé layer onto buttercream and peel off parchment, then gently spread with 1 1/4 cups coffee buttercream.

Repeat layering, ending with coffee buttercream (there will be some leftover). Chill at least 1 hour (after that, wrap in plastic wrap). Trim all around cake with a long sharp knife to neaten edges. Bring to room temperature (about 1 hour) before serving.

bring 1 3/4 cups sugar and water to a boil in a 3 qt heavy sauce pan over medium heat, stirring until sugar has dissolved, then wash down any sugar crystals from side of pan with a pastry brush dipped in cold water. Boil, without stirring, until it registers 220 to 225 F, 15 to 20 minutes.

At this point, while continuing to boil syrup, beat whites with espresso powder, vanilla, cream of tartar, and salt in mixer at medium speed until they just hold soft peaks. Add remaining 1/4 cup sugar, 1 tbsp at a time, beating, and beat until whites just hold stiff peaks.

When syrup reaches soft-ball stage (238-242 F), immediately pour syrup in slow stream down side of bowl into whites (avoid beaters) while beating at high speed. Beat until completely cool, 25 to 30 minutes. With mixer at medium speed, add butter 1 tbsp at a time, beating well after each addition and until buttercream is smooth. (Mixture may look curdled before all butter is added but will come together at end).

Transfer 2 cups buttercream to a small bowl and stir in chocolate. If buttercreams are too soft to spread, chill, stirring occasionally.