2 3/4 cups heavy cream, divided
8 ounces white-chocolate chips
1 Chocolate Crumb Pie Crust, blind baked (recipe follows)
5 ounces dark-chocolate chips
1 cup whole milk
1 whole egg, plus 1 yolk
1/4 cup sugar
3 tablespoons cornstarch
1 tablespoon vanilla extract or vanilla-bean paste

To prepare white-chocolate ganache, in a small pan or microwave-safe dish, heat 1/2 cup of the cream until simmering. Add the white chocolate and let sit 2 minutes. Stir until chocolate is melted and mixture is smooth. Pour into the pie crust and refrigerate until firm, about 30 minutes.

To make dark-chocolate ganache, in a small pan or microwave-safe dish, heat 3/4 cup cream until simmering. Add the dark chocolate and let sit 2 minutes. Stir until chocolate is melted and mixture is smooth. Pour over white-chocolate layer and refrigerate until firm, about another 30 minutes.

To make vanilla mousse, in a medium saucepan over medium heat, heat the milk until simmering.Meanwhile, in a medium bowl, whisk together the whole egg, yolk, sugar and cornstarch. When milk comes to a simmer, slowly pour it into egg mixture while whisking continuously. Return mixture to pan and whisk continuously over medium heat until mixture comes to a boil.

Transfer mixture to bowl, press plastic wrap directly onto surface of custard and refrigerate until no longer hot, about 30 minutes. When custard has cooled, stir in the vanilla extract or paste.

In a large bowl, use an electric mixer to beat remaining 1 1/2 cups cream to firm peaks. Fold half of whipped cream into cooled vanilla custard. Repeat with remaining whipped cream, folding gently but thoroughly to avoid deflating cream. Spoon vanilla mousse over chocolate ganache, then refrigerate until ready to serve.

Makes 8 servings.

CHOCOLATE CRUMB PIE CRUST: In a medium bowl, toss together 1 1/2 cups finely crushed chocolate cookie crumbs and 3 tablespoons granulated or brown sugar. Stir in 6 tablespoons melted butter until all crumbs are moistened. Stir in 1/2 cup toasted, finely chopped nuts, if desired. With back of a spoon or bottom of a measuring cup, press crumb mixture into a pie pan across bottom and up sides. Bake, unfilled, at 350 F for 15 minutes. Makes 1 (9-inch) crust.