Chop the chocolate and melt it with butter in a pot at low heat, stirring from time to time. Let it cool down a little. Crush the chestnuts in a tall container with a blender.
Preheat oven (electric cooker: 200 °C/circulating air: 180 °C/gas: see manufacturer). Separate eggs. Beat egg whites until stiff, adding 1 pinch of salt and sugar. Mix egg yolk, orange peel, 120 g chestnut cream and chestnut crumbs. Stir in chocolate mixture. Mix flour and baking powder, stir in briefly. Fold the beaten egg white in 2 portions into the chocolate dough.
Put the dough into a greased springform pan (20 cm Ø) and smooth it down. Bake in the oven for 40-45 minutes. After about 30 minutes, cover with baking paper if necessary. Take out, prick the base several times with a wooden skewer. Sprinkle with liqueur. Let it cool down.
Whip 450 g cream until very stiff, fold into 250 g chestnut cream. Remove the base from the mould. Spread the cream dome-shaped on the base. Whip 300 g cream until stiff, allow cream stiffener to trickle in. Pour cream into a piping bag with a perforated spout and squirt it onto the chestnut cream in patches close together. Chill the cake for about 1 hour.