Torta Setteveli (Seven-Layer Chocolate Cake)

Instructions

1. Sponge: Heat the oven to 350°F (175°C) and line the bottom of the springform pan with parchment. Whip the eggs and granulated sugar until pale and tripled in volume, 6 to 8 minutes. Sift the all-purpose flour and unsweetened cocoa powder over and fold in gently. Spread in the pan and bake until springy and the edges pull away, 12 to 15 minutes. Cool completely, about 30 minutes, then remove from the pan.
2. Clean the springform ring, set it closed on a flat serving board or tray and line the sides with the acetate collar. Fit the cooled sponge in the bottom, trimming if needed.
3. Crunch: Melt the milk chocolate in short bursts in the microwave or over simmering water, stir in the hazelnut praline paste, then fold in the crisp rice cereal. Spread evenly over the sponge and refrigerate until firm, 20 minutes.
4. Chocolate mousse, first layer: Make the mousse in two batches, using half of each mousse ingredient each time. Bring half the whole milk just to a simmer, pour over half the dark chocolate, wait 1 minute and stir until smooth; cool to about 95°F (35°C). Whip half the heavy cream to soft peaks and fold it into the chocolate in 2 additions. Spread over the crunch, level and refrigerate until set, about 45 minutes.
5. Hazelnut cream: Sprinkle the powdered gelatin over the cold water and let it soak 5 minutes. Heat the whole milk until steaming. Whisk the egg yolks and granulated sugar, slowly whisk in the hot milk, return to the pan and cook over low heat, stirring, until it coats a spoon and reaches 175 to 180°F (80 to 82°C), 4 to 6 minutes. Off the heat, stir in the soaked gelatin and pure hazelnut paste until smooth; cool to room temperature, stirring now and then, about 20 minutes.
6. Whip the heavy cream for the hazelnut cream to soft peaks and fold it into the cooled hazelnut custard. Spread over the set chocolate mousse and refrigerate until set, about 45 minutes.
7. Chocolate shards: Melt the dark chocolate for the shards, spread it very thinly on parchment and refrigerate until hard, 15 minutes. Break into small shards and scatter them over the hazelnut cream.
8. Chocolate mousse, second layer: Make the second batch of mousse with the remaining whole milk, dark chocolate and heavy cream exactly as before. Spread over the shards, smooth the top with an offset spatula and freeze the cake until solid, at least 6 hours or overnight.
9. Glaze: Soak the powdered gelatin in the cold water for 5 minutes. Bring the water, granulated sugar and heavy cream to a boil, whisk in the unsweetened cocoa powder and simmer, whisking, for 1 minute until glossy. Off the heat, stir in the soaked gelatin, strain and cool to 95°F (35°C), about 30 minutes.
10. Unmold the frozen cake, peel off the acetate and set it on a rack over a tray. Pour the glaze over the top in one go so it runs down the sides, smooth the top once with a spatula and move the cake to a serving plate. Refrigerate until thawed through, about 3 hours, before slicing with a hot knife.