This is more accurately a bavarois cake. For this recipe you'll need a 6" cake ring 2.5" high, or a cake pan of the same dimensions, but it's easy to make it in a 9" cake ring, springform, or cake pan: simply double the quantities listed here. If using a cake ring, a strip of acetate at least 2.5" wide and at least 19" long is recommended to make a clean side. If you don't have acetate, just freeze the cake for longer and unmold when very firm. It will be difficult to add the cocoa mirror glaze if using a cake pan without destroying the pristine sides, but you can build the layers any order you want, and decorate some other way, such as with white/dark chocolate shavings or peaks of whipped cream.
Creme Anglaise Base
120g (1/2 cup) whole milk
2 large egg yolks
15g (1-1/2 tablespoons) sugar
25g (1-1/2 tablespoons) light corn syrup
In a small saucepan over medium heat, bring the milk to a boil. In a separate small bowl, whisk the egg yolks, sugar, and corn syrup. Slowly pour the milk into the yolks in a thin stream while whisking madly. Return the mixture to the saucepan and reduce the heat to low. Stir constantly with a wooden spoon until it is thick enough to coat the back of the spoon and leave a trail when you run your finger through it (it will take a little more than a minute). Remove from heat and strain into a bowl. You will need the creme anglaise to be hot enough to melt the chocolate in the next step, so work quickly.
Chocolate Mousses
55g (1-3/4 oz) white chocolate, chopped
55g (1-3/4 oz) milk chocolate, chopped
63g (2 oz) 72% chocolate, chopped
375g (1-1/2 cup plus 1 tablespoon) heavy cream, chilled
and for each chocolate mousse:
1/2 teaspoon powdered unflavored gelatin
15g (1 tablespoon) cold water
Prepare 3 medium bowls each containing one type of chocolate and 3 small cups, one for each type of chocolate. Sprinkle the gelatin over the water and let stand for 2 minutes. Microwave on low power for 15 seconds, or until the gelatin is fully dissolved. Dump 1/4 cup (60g) of the hot creme anglaise over each type of chocolate and give each a gentle stir to melt the chocolate. Stir in the dissolved gelatin into each chocolate sauce and stir until well-combined. Set aside.
In a well-chilled bowl and using well-chilled beaters, whip the cream until it holds medium peaks, about 5 minutes. When not using the whipped cream, keep it in the fridge.
Line the sides of a 6" cake ring with acetate and place on a piece of plastic wrap large enough to cover the bottom of the ring on a rimless baking sheet or removable bottom of a tart pan. If using a cake pan, spray with vegetable cooking spray and line with a large piece of plastic wrap, pressing it against the sides.
Take a third of the whipped cream (125g) and fold it into the dark chocolate sauce until well-combined. Pour it into the center of the ring and give it a gentle bang to level the mousse. Place in the freezer for about 20 minutes or until halfway firm. Take half of the remaining whipped cream (125g) and fold it into the milk chocolate sauce until well-combined. Pour it into the center of the firm dark chocolate mousse and give it a gentle bang to level the mousse. Return to the freezer for 20 more minutes. Fold the white chocolate sauce into the remaining whipped cream until well-combined. Pour it into the center of the firm milk chocolate mousse, taking care to leave a few mm space to pour in the cocoa glaze (eat the remaining white chocolate mousse if there is any as a treat). Leave in the freezer overnight, or until completely firm.
Cocoa Mirror Glaze
60g (1/4 cup) whole milk or heavy cream
75g (5 tablespoons) water
90g (7 tablespoons plus 1/2 teaspoon) granulated sugar
33g (5 tablespoons plus 1/2 teaspoon) Dutch-processed cocoa powder, preferably Valrhona
3g (1/2 packet) gelatin granules
15g (1 tablespoons) water
Prepare the glaze according to the instructions for glacage here. You will have enough for two cakes. Pour the glaze into the remaining space of the cake ring and place in the freezer for 20 minutes, or until set.
To unmold the mousse, place a 6" cake board (you could just use a 6" circle of stiff cardboard coated with aluminum foil) under the dessert and ease the plastic wrap away. Push from the bottom to release the mousse from the ring. Peel away the acetate and place on a serving platter. If you've used a cake ring, simply invert it into a serving platter and peel away the plastic wrap. Let it thaw in the fridge for a few hours before serving. I decorated the top with melted white chocolate.
recipe from no special effects: