Chocolate Mousse Cake with Chocolate Ganache (Polish Rigo Jancsi)

This classic Hungarian dessert consists of two layers of chocolate sponge held together by a luscious, mousse-like cocoa cream filling which is sometimes flavoured with a splash of dark rum, while the cake itself is typically covered in a rich dark chocolate ganache. Rigo Jancsi is said to have been invented at the turn of the 20th century and named after a famous Hungarian Gypsy violinist who seduced and eventually married Clara Ward, the daughter of an American millionaire named Eber Brock Ward and the wife of Belgian Prince de Caraman-Chimay. The two lovers met while Rigo performed with his orchestra in a posh Paris restaurant which was frequented by a number of Belgian aristocrats. Legend has it that Clara was instantly fascinated by Rigo's music, but even more so mesmerized by his passionate black eyes.

Ganache and Topping:
4 cups heavy cream
¼ cup (½ stick) unsalted butter
¼ cup sugar
20 oz semisweet chocolate, finely chopped
2 oz chocolate, chopped separately will use it for the topping
⅓ cup dark rum
2 tsp. pure vanilla extract

Syrup:
¼ cup water
2 Tbsp. granulated sugar
2 Tbsp. dark rum

Cake:
1½ tsp. pure vanilla extract
¾ tsp. instant coffee powder
⅔ cup all-purpose flour, unbleached
3 Tbsp. unsweetened cocoa powder
½ tsp. baking soda
3 large eggs, separated
¾ cup granulated sugar
¼ tsp kosher salt

Make the Chocolate Ganache:
Stir the heavy cream, butter, and sugar together in a saucepan.

Place the saucepan over medium heat and heat it up until the sugar dissolves and the heavy cream comes to a simmer. Remove from heat. Add 20 oz of chocolate. Whisk until melted and smooth. Whisk in rum and vanilla.

Transfer one cup of the warm mixture to a small bowl and add the 2 oz chocolate to it. This will be the final glaze. Mix until smooth. Set aside. Transfer the rest of the chocolate mixture into a larger bowl to use as filling.

Chill until cold and thick, at least 6 hours.

Make the Syrup: (It will be used to flavour and make the cake moist)
Bring water and sugar to a boil. Remove and let cool. Mix in the rum.

Preheat oven to 350°F (180°C/160°C fan, Gas Mark 4). Line bottom of a 9x9" pan with parchment paper and then butter the paper.

Make the Cake:
Combine vanilla and coffee powder in a cup and mix to dissolve the coffee.

Sift flour, cocoa, and baking soda together into a bowl.

Using an electrical mixer, beat the egg yolks and ½ cup sugar in medium bowl until they get very thick and light in colour. Beat in the vanilla-coffee mixture.

Use clean dry beaters to beat egg whites and salt until soft peaks form in another bowl. Add remaining ¼ cup sugar, beating until stiff but not dry.

Fold ½ of egg whites into yolk mixture. Fold in half of flour mixture. Fold the remaining whites, then remaining flour mixture.

Transfer batter to prepared pan and spread gently to an even thickness.

Bake cake for about 18 minutes until it puffs up and a toothpick inserted into the center comes out clean.

Cool in pan on rack. It might shrink a little bit.

Assemble the Cake:
Cut around the pan to loosen up the cake. Turn out onto the work surface and peel off parchment paper.

Using a long serrated knife, cut cake horizontally in half.

Place 1 half, cut side up, on a platter. Use a pastry brush to brush syrup over the cake surface.

Using an electric mixer, beat cold chocolate ganache until thick and lighter in colour, less than 1 minute. Spread all filling evenly over the cake layer, aligning with sides of cake.

Brush with syrup the other half of cake, the cut side one.

Place layer, syrup side down, on top of the chocolate ganache.

Rewarm the preserved cup of ganache over low heat until pourable. Pour it over the top of the cake, starting in the center.

Use a spatula and spread topping to edges, trying to not spill over.

Chill cake overnight, covering loosely with foil or with cake dome after 2 hours.

Keep refrigerated but serve it at room temperature.

Makes 12 servings.