Prep time: 25 minutes
Cook time: 1 hour
To get started on this recipe, the first things you should do are to make the coffee for the frosting and to separate the eggs for the cake batter. Eggs will separate better when they are cold, right out of the refrigerator, but will whip up better if they are at room temp. So separate them first, and then prep the rest of the ingredients.
1 cup (200 g) white granulated sugar (divided into 3/4 cup and 1/4 cup)
1 cup (120 g) finely ground walnuts (from about 1 1/3 cup of shelled walnuts)
1/2 cup (55 g) fine dry bread crumbs (plain, unseasoned)
1/2 cup (100 g) white granulated sugar
2 Tbsp corn starch
1 cup (8 fluid ounces, 236 ml) strong coffee (I use decaf, with twice the amount of coffee for the liquid as I would usually use to drink)
1 ounce (30 g) of chocolate chips (a little less than 1/4 of a cup)
1 Tbsp butter
2 teaspoons vanilla extract
1 cup (8 fluid ounces, 236 ml) heavy whipping cream
1 Separate the eggs, into yolks and whites (see How to Separate Eggs). Take care to make sure there are no pieces of shell or egg yolk in the whites, and that the bowl you are using to contain them is completely clean with no residue of fat. Any fat from yolks or oil will make it difficult to beat the egg whites.
2 Prepare two 9-inch cake pans. Line the pans with parchment paper or wax paper. Lightly butter the sides of the pans (not the paper).
3 Preheat oven to 350°F (175°C). Mix together the ground walnuts and the bread crumbs in a small bowl and set aside.
4 Place the egg yolks into a mixing bowl and beat until smooth. Slowly add 3/4 cup of white sugar and continue to beat the egg yolks until thick and pale. (I use a hand mixer for this.)
5 Using a stand mixer, beat the egg whites with the whisk attachment until foamy. Slowly drizzle in 1/4 cup of white sugar, and beat until soft peaks form.
6 With a rubber spatula, gently fold the egg whites into the yolk mixture, alternately with the walnut mixture.
7 Spoon the batter into the prepared, parchment-layered cake pans. Bake for 25 to 30 minutes at 350°F (175°C) until a slight imprint remains when touched.
8 While the cake is cooking prepare the mocha frosting base. Place 1/2 cup of white sugar and 2 tablespoons of cornstarch into a saucepan. Turn the heat onto medium and gradually stir in the coffee and the chocolate chips. Stir continuously until the mixture starts to simmer and thicken quite substantially. Continue to stir while the mixture simmers for 1 minute. Then remove from heat and stir in the butter and vanilla extract until well blended. Let cool completely. (You will incorporate this mocha base into whipped cream when you frost the cake.)
9 Remove the cakes from oven and cool in the pans for 10 minutes. Run a dull knife around the edges of the cakes to separate it from the sides of the pans. Carefully invert the cakes onto a rack. Carefully peel back and discard the parchment or wax paper. Let cool completely. Note that if you want to make ahead, you can cook the cakes first, let cool to room temp, wrap with plastic wrap, and freeze until you are ready to frost and serve.
10 Complete the frosting. Whip the cream until it is rather thick, just before that point to which if you kept on whipping it would turn to butter. This will help it hold up as a frosting. Once whipped, fold the whipped cream and mocha base together. It may be a little speckled, and if you fold it only lightly, you can have almost a marbling effect of light and dark with the frosting, if you wish. Place one cake on a serving platter. Frost the top. Place the second cake on top of it, and frost the top and sides of the cake. Serve immediately, or keep chilled until serving.