This recipe also requires a jar of peeled, roasted chestnuts. I used two vacuumed packs of peeled and roasted chestnuts that you can find at most Asian markets. They are quite cheap too. I think I bought a pack for $1 or $2 each.
Chocolate-Chestnut Mousse Cake
adapted from Martha Stewart Living
Vegetable oil, for pan
1 jar (7.4 ounces) peeled, roasted chestnuts
1 cup whole milk
1 teaspoon of pure vanilla extract
1/4 cup plus 1 tablespoon light-brown sugar
pinch of coarse salt
3 large egg yolks
1 tablespoon cornstarch
1 teaspoon unsalted butter, room temperature
2 ounces bittersweet chocolate (preferably 61 cacao), melted and slightly cooled, plus more for shavings
1 1/2 cold heavy cream
24 chocolate wafer cookies (from 1 package)
Slowly add hot chestnut mixture to the yolk mixture, whisking constantly. Return the chestnut and egg mixture to the pan and cook over medium-low heat. Whisk until thick, about 2 minutes. Transfer to a bowl of a mixer, add vanilla and butter and beat on medium speed until cool, about 5 minutes. I just did this by hand (one less bowl to clean later).
When you slice into it, you'll see the three layers of chocolate, chestnut and whipped cream.