Chocolate-Chestnut Mousse Cake

From Martha Stewart - This stunning dessert is a simple-to-make icebox cake. Chocolate shavings are easily made with a vegetable peeler.

• Ready In: 2 hrs 15 mins
• Serves: 8
• Yields: 1 8 in cake

Ingredients

•  vegetable oil, for pan
• 1 (7 1/2ounce) jar  peeled  roasted chestnuts
• 1  cup  whole milk
• 1⁄4 cup  plus 1 tablespoon light-brown sugar
• 1  pinch coarse salt
• 3  large  egg yolks
• 1  tablespoon cornstarch
• 1  teaspoon pure vanilla extract
• 1  tablespoon unsalted butter, room temperature
• 2  ounces bittersweet chocolate, melted and slightly cooled, plus more for shavings (preferably 61 percent cacao)
• 1 1⁄2 cups  cold heavy cream
• 24  chocolate wafer cookies (from 1 package)

Directions

1. Lightly coat an 8-inch round cake pan with oil, and line with plastic, leaving a 4-inch overhang.
2. Finely grind chestnuts in a food processor. Heat ground chestnuts, milk, 3 tablespoons sugar, and the salt in a medium saucepan over medium-high heat, stirring occasionally, until bubbles form at edge.
3. Whisk together yolks, cornstarch, and remaining 2 tablespoons sugar in a medium heatproof bowl.
4. Slowly add hot chestnut mixture to yolk mixture, whisking constantly. Return to pan; cook over medium-low heat, whisking constantly, until thick, about 2 minutes. Transfer to the bowl of a mixer. Add vanilla and butter. Beat on medium speed until cool, about 5 minutes. Stir half the chestnut mixture into melted chocolate.
5. Beat 1 1/4 cups cream until soft peaks form. Using a rubber spatula, gently fold half the whipped cream into plain chestnut mixture and the other half into chocolate-chestnut mixture.
6. Pour chestnut mousse into prepared pan. Cover with 12 chocolate wafers, working in a circular pattern. Top with chocolate-chestnut mousse and remaining 12 chocolate wafers. Fold plastic overhang over top to cover cake. Refrigerate overnight.
7. Uncover cake; place a platter on top, flip, and unmold. Remove plastic. Beat remaining 1/4 cup cream until soft peaks form. Spread on top of cake. Garnish with chocolate shavings.