Make the white chocolate mousse:
In a bowl whisk together well the yolks, the sugar, and a pinch of salt, add the cornstarch, sifted, and whisk the mixture until it is just combined. Add the milk, scalded, in a stream, whisking, transfer the mixture to a heavy saucepan, and boil it, whisking, for 1 minute, or until it is very thick and smooth. Strain the pastry cream through a fine sieve into a bowl, stir in vanilla and the butter, and chill the pastry cream, its surface covered with plastic wrap, until it is cooled completely. In a metal bowl set over barely simmering water melt the white chocolate, stirring occasionally, and let it cool to lukewarm. In a large bowl whisk together the white chocolate and 1 cup of the pastry cream, reserving the remaining pastry cream for the raspberry mousse, until the mixture is combined well. In a bowl with an electric mixer beat the heavy cream until it holds soft peaks, whisk one fourth of it into the white chocolate mixture, and fold in the remaining whipped cream gently but thoroughly.
Line the sides of an oiled 9 1/2-inch springform pan as smoothly as possible with pieces of plastic wrap (the plastic wrap prevents the filling from discoloring and makes unmolding the cake easier), letting the excess hang over the side, and put an 8-inch cardboard round in the bottom of the pan. Invert the top layer of the génoise onto the round, brush the cake with some of the framboise, and spread it evenly with half the white chocolate mousse (about 2 cups). Invert the middle layer of the génoise onto the mousse, brush it with some of the remaining framboise, and chill the cake and the remaining white chocolate mousse while preparing the raspberry mousse.
Make the raspberry mousse:
In a blender or food processor purée the raspberries with the reserved syrup and strain the purée through a fine sieve set over a metal bowl, pressing hard on the solids. In a small saucepan sprinkle the gelatin over the framboise and let it soften for 1 minute. Heat the mixture over moderately low heat, stirring, until the gelatin is dissolved and whisk it into the purée. Whisk the reserved pastry cream into the raspberry mixture, whisking until it is smooth, set the bowl in a larger bowl of ice and cold water, and whisk the mixture until it is the consistency of raw egg white. Remove the bowl from the ice water and in a bowl with an electric mixer beat the heavy cream until it holds soft peaks. Whisk one fourth of the whipped cream into the raspberry mixture and fold in the remaining whipped cream gently but thoroughly.
Spread about 1 cup of the raspberry mousse evenly over the middle layer of génoise in the pan, arrange some of the raspberries neatly around the edge of the pan, and continue to arrange the raspberries in concentric circles until the surface of the mousse is covered. Spread the remaining raspberry mousse over the raspberries, invert the third layer of génoise onto the mouse, and brush it with the remaining framboise. Spread the remaining white chocolate mousse over the génoise (the pan will be completely full) and chill the cake, its surface covered with a sheet of wax paper, for at least 6 hours or overnight. Remove the side of the pan, peel the plastic wrap carefully from the side of the cake, and transfer the cake with a spatula to a serving plate.
Garnish the cake:
Arrange some of the raspberries around the top edge of the cake, mound the white chocolate curls in the center, and garnish the bottom edge of the cake with the remaining raspberries and the mint sprigs.
Make the white chocolate génoise:
Line the bottom of a greased 8 1/2-inch springform pan with wax paper, grease the paper, and dust the pan with flour, knocking out the excess. In a metal bowl set over a pan of barely simmering water melt the white chocolate with the butter, the vanilla, and 3 tablespoons water, stirring until the mixture is smooth. Remove the bowl from the heat and let the mixture cool. Into a bowl sift together the flour and the salt. In a large bowl with an electric mixer beat the eggs with the sugar on high speed for 5 minutes, or until the mixture is triple in volume and forms a ribbon when the beaters are lifted. Fold the flour mixture into the egg mixture until the batter is just combined and fold in the white chocolate mixture gently but thoroughly. Pour the batter into the pan, smoothing the top, and bake the cake in the middle of a preheated 350°F. oven for 25 minutes, or until a tester comes out clean. Transfer the cake to a rack, run a sharp knife around the edge, and remove the side of the pan. Invert the cake onto another rack and remove the wax paper. Reinvert the cake onto the rack and let it cool completely.