1. Preheat oven to 350ºF and adjust rack to middle position. Place almond flour, coconut flour, cocoa powder, gelatin, arrowroot and sea salt in the bowl of a food processor. Pulse 2-3 times to combine. Add maple syrup and butter and process until dough forms a ball. Press dough into the bottom of a 9-inch spring form pan. Bake for 12 minutes. Cool.
2. Place ground chestnuts, milk, 2 tablespoons maple syrup and salt in a medium saucepan over medium heat. Bring to a simmer, stirring occasionally. In a medium bowl, whisk egg yolks, arrowroot and remaining 2 tablespoons maple syrup. Using a ladle, slowly add a spoonful of the hot chestnut mixture to the yolk mixture, whisking constantly. Slowly add now tempered yolk mixture to the hot chestnut mixture, whisking constantly. Continue to cook and whisk until thick like pudding, about 3 minutes. Pour mixture into the bowl of a mixer, add butter and vanilla and beat for 5 minutes on medium speed. Pour half of chestnut mixture into a medium bowl. Whisk melted chocolate into 1/2 of the chestnut mixture. Pour chocolate/chestnut mixture over the cookie crust. Using an offset spatula, spread evenly over crust. Whip 1 cup of heavy cream until soft peaks form. Fold into remaining chestnut mixture and spread over the chocolate/chestnut mixture. Cover with plastic wrap and place in the freezer for 6 hours.
3. Run a knife around the edge of the cake and then release from the pan. To serve, whip remaining 1/2 cup cream and spread overtop of cake. Garnish with cocoa powder or chocolate shavings.

*If you’d like to make your own chocolate, you can combine 2 tablespoons melted unsalted butter or coconut oil, 6 tablespoons cocoa powder, and 1 tablespoon maple syrup.