In a small saucepan, combine chestnuts, water, and sugar. Bring to a boil and boil for 20 minutes. Remove from heat and let cool slightly.

Add chestnuts and some of the sugar-water to a food processor and blend. Add a little more water at a time until you have a smooth paste-like consistency.

Melt chocolate.

In the bowl of an electric mixer, beat non-dairy whipped topping. Add melted chocolate and half the chestnut paste. Combine.

Preheat oven to 350 degrees Fahrenheit. Line a 10-inch round (or nine-inch square) baking pan with Gefen Parchment Paper and grease (you can also use individual ramekins).

Place chocolate in a glass or ceramic bowl. Heat non-dairy whipped topping in a small saucepan. Bring to a boil and pour over chocolate. Let sit for a minute to let the chocolate melt, then stir to combine. (You can put it in the microwave for 30 seconds if there’s still bits of chocolate that won’t melt).

Let cool a bit, then whisk in the egg and remaining chestnut paste.

Pour ganache mixture into prepared baking pan (or individual ramekins) and bake for 20 minutes, or until middle is firm. Remove from oven and let cool.

You can remove ganache cake from baking pan and pipe mousse onto cake, or cut the cake into squares and layer with mousse (it doesn’t have to be three layers, they can be smaller).

Cut extra scraps of the ganache cake into triangles to use as a garnish. I also rolled pieces of chestnuts in sugar and used those as a garnish too.