Le Jour at la Nuit Hotel de Crillon

This recipe is almost too good to share. Selfish, I know. It has become somewhat of a trademark dessert for me. But as much as I would like to take credit for this, it is not an original recipe. A friend in Rochester, NY first made this recipe for one of her many movie nights. Marc, being the chocolate lover the he his, thought he had died and gone to heaven. Seriously. Word of this recipe got out and it became quite a hot commodity. It sold at a ward auction for $75! I believe she got the recipe from Bon Appetite magazine, but it wasn't until we moved away that my begging finally resulted in her sharing the recipe with me.
This is quite an intense recipe, with many steps and days involved. I only make it once or twice a year--this year Marc gets it for Father's Day (hence, the tie design on top). If anyone actually makes this recipe, I would love to hear about it.
WARNING: This should only be eaten by those who consider themselves true chocolate lovers--this is NOT for the faint of heart!

Le Jour et la Nuit Hotel de Crillon (White and Dark Chocolate Mousse Cake)
(thanks to April Holmes, for changing our lives with this recipe!)

9 large egg yolks
1 c. sugar
6 Tblspn. cornstarch
3 c. milk, scalded
1 Tblspn. vanilla
14 oz. fine-quality bittersweet chocolate, chopped
4 c. well chilled heavy cream
14 oz. fine-quality white chocolate, chopped

Garnish:
6 oz. fine-quality white chocolate, grated
4 oz. fine-quality bittersweet chocolate, grated

In a large bowl whisk together the egg yolks and the sugar until mixture is combined well, add the cornstarch (sifted) and whisk the mixture until it is just combined.
Whisk in the scalded milk in a slow stream, transfer the mixture to a heavy saucepan, and bring to a boil, whisking constantly.
Boil the pastry cream, whisking, for 1-2 minutes, or until it is very thick and smooth, strain it through a fine sieve into a heatproof bowl and stir in the vanilla.
Lay piece of plastic wrap on the pastry cream for 1-2 hours, or until it is completely cooled.
In the top of a double boiler, melt the bittersweet chocolate, stirring occasionally, and let it cool until it is lukewarm.
Transfer half of the pastry cream to a large bowl, whisk in the chocolate and whisk the mixture until it is well combined.
In a chilled bowl, with an electric mixer, beat 2 cups heavy cream until it holds soft peaks, stir in ¼ of it into the chocolate mixture, and fold in the remaining whipped cream gently, but thoroughly.
Pour the dark chocolate mousse into a lightly oiled 10-inch springform pan, and spread evenly. Chill while making the white chocolate mousse.
Repeat the above process for the white chocolate (melting, mixing it in the pastry cream, adding the heavy cream, and then spreading it on top of the dark chocolate mousse)
Cover the cakes loosely with parchment paper or wax paper and chill overnight.
Run a thin knife around the edge of the cake, remove the side of the pan and smooth the side of the cake with a spatula.
Put the cake on a rack set in a shallow baking pan, press the grated white chocolate onto the side, gathering the excess in the pan and reapplying it until the side is completely coated evenly.
Transfer the cake to a serving platter. Mound the white chocolate carefully on half the cake and the dark chocolate on the other half of the cake. Chill again until ready to serve.