Kaffeehaus: Exquisite Desserts from the Classic Cafes of Vienna, Budapest, and Prague [Anglais] [Relié]

Hungary's national chocolate dessert, Rigó Jancsi consists of squares of cocoa mousse sandwiched between chocolate cake and covered with a shiny chocolate glaze.

CAKE
1/2 cup all-purpose flour
3 tablespoons Dutch-processed cocoa powder
1/4 teaspoon salt
3 tablespoons milk
3 tablespoons vegetable oil
1/2 teaspoon vanilla extract
3 large eggs, at room temperature
2/3 cup sugar
FILLING
2 tablespoons golden rum or water
1 1/2 teaspoons unflavored powdered gelatin
1 teaspoon vanilla extract
1/2 cup confectioners' sugar
1/4 cup Dutch-processed cocoa powder
2 cups heavy cream

GLAZE
1/4 cup hot water
3 ounces high-quality semisweet chocolate, finely chopped
1 tablespoon unsalted butter, at room temperature

1. To make the cake: Position a rack in the center of the oven and heat to 350°F. Lightly butter a 15 x 11-inch jelly roll pan, and line the bottom and sides with parchment or wax paper. (Cut slashes in the corners of the paper to help them fold neatly.) Lightly butter the paper.

2. Sift the flour, cocoa, and salt together into a bowl. Mix the milk, oil, and vanilla in a measuring cup.

3. Crack the eggs into a medium bowl and add the sugar. Using an electric mixer on high speed, beat until very light in color and texture, about 2 minutes. Sift half of the flour mixture over the eggs and fold in. Fold in half of the milk mixture. Repeat with the remaining flour and milk mixtures. Spread evenly in the pan, being sure the batter fills the corners.

4. Bake until the cake springs back when pressed in the center, about 15 minutes. Cool for 5 minutes on a large wire rack. Invert onto the rack and peel off the paper. Cool completely.

5. To make the filling: Pour the rum into a small bowl and sprinkle with the gelatin. Set aside for 5 minutes. Place the bowl in a skillet of gently simmering water. Using a small rubber spatula, stir constantly until the gelatin is completely dissolved, being sure to wipe down any undissolved gelatin on the sides of the bowl. Remove the bowl from the water, stir in the vanilla, and set aside to cool slightly.

6. In a bowl, combine the confectioner's sugar and cocoa. In a chilled medium bowl, beat the cream until it just begins to thicken. Sift the cocoa mixture into the cream and beat until barely stiff. Stir about one third of the whipped cream into the gelatin mixture, then beat back into the cream, beating until the filling is very stiff. (But do not overbeat, or it will separate.)

7. Cut the cake into two 7 1/2-inch-wide pieces. Place one cake on a baking sheet. Spread all of the filling on the cake in a thick layer, smoothing the sides. Refrigerate while making the glaze.

8. To make the glaze: Combine the water and chocolate in a small saucepan. Cook over low heat, stirring constantly with a rubber spatula, until the chocolate is almost melted. Remove from the heat and let stand, stirring occasionally, until the chocolate is completely melted. Add the butter and stir until melted and combined. Set aside to thicken and cool slightly.

9. Place the remaining cake layer, smooth side up, on a wire rack set over a jelly roll pan. Pour all of the glaze on top of the cake. Using a metal spatula, smooth and coax the glaze over the sides of the cake. Refrigerate until the glaze is set, about 15 minutes.

10. Using a thin sharp knife rinsed under hot water between cuts, cut the glazed cake into 9 rectangles. Following their original positions, arrange the rectangles on top of the filling. Refrigerate until the filling is set, about 1 hour. Cut between the rectangles to make individual servings. Serve chilled.

MAKE AHEAD

The mousse squares can be prepared up to 2 days ahead and stored under a cake dome in the refrigerator.