Note: This cake only takes 2 hours to prepare but does need to chill for at least 3 hours before serving so be sure to start well in advance of when you plan to serve it.
For the Cake:
2 cups cake flour
2 tsp. baking powder
1/8 tsp. baking soda
1/4 tsp. salt
1 1/4 sticks (10 tbsp.) unsalted butter, at room temp.
1 cup sugar
3 large eggs
1 large egg yolk
1 1/2 tsp. pure vanilla extract
3/4 cup buttermilk
For the Espresso Extract
4 tbsp. instant espresso powder
4 tbsp. boiling water
For the Espresso Syrup
1 cup water
2/3 cup sugar
2 tbsp. amaretto, Kahlua, or Brandy
For the Filling and Frosting
1 8-ounce container of mascarpone
1/2 cup confectioners’ sugar, sifted
1 1/2 tsp. pure vanilla extract
1 tbsp. amaretto, Kahlua or brandy (I used the espresso syrup instead)
1 cup cold heavy cream
2 1/2 ounces bittersweet or semisweet chocolate, finely chopped (I used milk chocolate since I wanted something less bitter to contrast with the coffee)
How to make it
GETTING READY: Center a rack in the oven and preheat to 350 degrees F. Butter two 9-x-2-inch round cake pans, dust the insides with flour, tap out the excess and line the bottoms of the pans with parchment or wax paper. Put the pans on a baking sheet.
TO MAKE THE CAKE: Sift together the cake flour, baking powder, baking soda and salt.
Working with a stand mixer, preferably fitted with a paddle attachment, or with a hand mixer in a large bowl, beat the butter on medium speed until soft and creamy. Add the sugar and beat for another 3 minutes. Add the eggs one by one, and the yolk, beating for 1 minute after each addition. Beat in the vanilla; and don’t be too concerned if the mixture looks curdled. Reduce the mixer to speed to low and add the dry ingredients in 3 additions and the milk in 2 (begin and end with the dry ingredients); scrape down the sides of the bowl as needed and mix only until the ingredients disappear into the batter. Divide the batter evenly between the two pans and smooth out the tops with a rubber spatula.
Bake for 28 to 30 minutes, rotating the pans at the midway point. When fully baked, the cakes will be golden and springy to the tough and a thin knife inserted into the center will come out clean. Transfer the cakes to a rack and cool for about 5 minutes, then run a knife around the sides of the cakes, unmold them and peel off the paper liners. Invert and cool to room temperature right side up.
TO MAKE THE EXTRACT: Stir the espresso powder and boiling water together in a small cup until blended. Set aside.
TO MAKE THE SYRUP: Stir the water and sugar together in a small saucepan and bring to a boil. Pour the syrup into a small heatproof bowl and stir in 2 tbsp. of the espresso extract and 2 tbsp. of the liqueur or brandy; set aside.
TO MAKE THE FILLING AND FROSTING: Put the mascarpone, sugar, vanila, and liqueur in large bowl and whisk just until blended and smooth.
Whisking with the stand mixer with the whisk attachment or with a hand mixer, whip the heavy cream until it holds firm peaks. Switch to a rubber spatula and stir about one quarter of the whipped cream into the mascarpone. Fold in the rest of the whipped cream with a light.
TO ASSEMBLE THE CAKE: If the tops of the cakes have crowned, use a long serrated knife and gentle sawing motion to even them. Place one layer right side up on a cake plate protected with strips of wax or parchment paper. Using a pastry brush or small spoon, soak the layer with about one third of the espresso syrup. Smooth some of the mascarpone over the layer — use about 1 1/4 cups — and gently press the chopped chocolate into the filling. Put the second cake layer on the counter and soak the top of it with half the remaining espresso syrup, then turn the layer over and position it, soaked side down, over the filling. Soak the top of the cake with the remaining syrup.
For the frosting whisk 1 to 1 1/2 tbsp. of the remaining espresso extract into the mascarpone filling. Taste the frosting as you go to decide how much extract you want to add. If the frosting looks as if it might be a little too soft to spread over the cake, press a piece of of plastic wrap against its surface and refrigerate it for 15 minutes or so. Refrigerate the cake too.
With a long metal icing spatula, smooth the frosting around the sides of the cake and over the top. Press the remaining chocolate shavings into the top of the cake.
Refriegerate the cake for at least 3 hours (or for up to 1 day) before serving — the elements need time to meld.