Toothpicks make excellent guides for cutting a cake into layers. Using a ruler, insert toothpicks at regular intervals around the side of the cake, dividing it into 2, 3 or even 4 horizontal layers. Placing one hand on top of the cake, and using a long, serrated knife positioned just above the line of toothpicks marking the layer, cut the cake with an even sawing motion. Lift off the top layer and carefully set it aside, then remove the row of toothpicks you used as a guide. If the cake has more than 2 layers, repeat to cut the additional layers.
For the cake:
- 5 eggs, separated, plus 1 egg yolk, at room temperature
- 2/3 cup granulated sugar
- 1 cup unbleached all-purpose flour
For the coffee sugar syrup:
- 1/4 cup granulated sugar
- 1 tsp. instant espresso powder
- 1/4 cup water
For the coffee meringue buttercream:
- 12 Tbs. (1 1/2 sticks) unsalted butter, at room temperature
- 3 egg whites, at room temperature
- 3/4 cup plus 3 Tbs. granulated sugar
- 3 Tbs. water
- 4 tsp. instant espresso powder, dissolved in 1 tsp. boiling water
- Confectioners’ sugar for dusting
- Candied coffee beans for decorating
Preheat an oven to 350°F. Generously butter a 6-cup charlotte mold.
To make the cake, in the bowl of an electric mixer fitted with the whisk attachment, beat the egg whites on medium speed until they start to foam. Add one-third of the granulated sugar and beat until the whites are opaque, then add another one-third of the sugar. When the whites start to become firm and increase in volume, add the remaining sugar and increase the speed to high. Beat until the whites form soft peaks but still look wet.
In another bowl, whisk the egg yolks by hand until blended. Using a large rubber spatula, carefully fold the yolks into the whites. Sift the flour over the egg mixture in 2 additions and carefully fold in.
Pour the batter into the prepared mold and smooth the top. Bake until the cake is browned and puffed and a skewer inserted into the center comes out clean, 20 to 25 minutes. Transfer the pan to a wire rack and let cool for 10 minutes, then unmold the cake. If necessary, tap the pan on the countertop to release the cake.
To make the coffee sugar syrup, in a small saucepan, stir together the granulated sugar and espresso powder. Add the water, place the pan over medium heat and bring to a boil, stirring occasionally until the sugar mixture dissolves. Remove from the heat and let cool to room temperature.
To make the coffee meringue buttercream, in a bowl, whisk the butter by hand until it is creamy; set aside. In the bowl of an electric mixer fitted with the whisk attachment, beat the egg whites on medium speed until they start to foam. Add 2 Tbs. of the granulated sugar and beat until the whites are opaque and then increase in volume.
Meanwhile, in a saucepan over medium heat, bring the 3/4 cup granulated sugar and the water to a boil, stirring a few times until the sugar dissolves. Using a damp pastry brush, brush down any crystals that form on the sides of the pan. Increase the heat to medium-high and cook the syrup, undisturbed, until it registers 240°F on a candy thermometer. While continuing to boil the syrup, increase the mixer speed to high and add the remaining 1 Tbs. granulated sugar to the egg whites.
When the syrup registers 250°F, remove it from the heat. With the mixer speed on high, pour the syrup into the whites in a thin stream, aiming for the side of the bowl. Reduce the speed to medium and beat until the meringue cools to room temperature and is stiff, about 5 minutes. Beat in the dissolved espresso, then beat in the butter in 3 additions, incorporating each addition before adding another. When all the butter has been added, increase the speed to medium-high and beat the buttercream until thick and smooth, about 1 minute. Use immediately.
Cut the cake into 4 equal layers (see note above). Put the widest layer, cut side up, on a serving plate. Brush with some of the coffee sugar syrup. Reserve about half of the buttercream for the outside of the cake. Spread a thin layer of the remaining buttercream on the layer. Continue to alternate layers of cake brushed with syrup and spread with buttercream. You will have 4 layers of cake and 3 layers of buttercream. The shape of the assembled cake will resemble that of the mold (and the original whole baked cake). Refrigerate the cake for 30 minutes.
Spread the reserved buttercream over the top and sides of the cake. Dust the cake with confectioners’ sugar and decorate with candied coffee beans. Refrigerate until ready to serve. Serves 6 to 8.