Prepare all ingredients:
Cook the chestnuts 20 minutes in boiling salted water. When finished, drain them and peel them.
Pass them through a food mill.
Add 200 g butter, 200 g caster sugar, 3 whole eggs and the vanilla to the still warm chestnut purée.
Mix well.
Pour half of the obtained mixture in a buttered baking mold. Store in the fridge.
Mix the almond powder with 75 g sugar, 1 egg yolk and the cocoa powder.
Add 75 g butter to this pommade.
Pour this preparation in the baking pan which contains the first mixture.
Cover with the rest of the chestnut preparation.
Place in the fridge for 4 hours.
Cream: Cook the sugar at 121°C.
Pour it on the egg yolks while beating with an electric whisk on low speed.
Whisk until completely cooled.
Add the softened butter...
...and finally the cooled melted chocolate.
Remove the cake from the pan...
...and coat with chocolate butter cream.
Decorate with grilled split almonds. Serve.