For the base, preheat the oven to 175 °C. Grate the marzipan finely and mix with the eggs. Sieve the cocoa and fold it in. Grease and flour a square form of about 24 cm side length with butter.
Pour in the dough, smooth it down and bake in the middle of the preheated oven for 10-12 minutes. Remove from the oven and allow to cool.
For the ice cream, lightly whip the cream. Beat the egg yolks and icing sugar until fluffy. Melt the chocolate at low wattage in the microwave or over a warm water bath, allow to cool slightly.
Then stir into the egg mixture. Add mint oil or liqueur and fold in the cream. Finely chop the mint and stir in. Spread the mixture on the completely cooled dough base, smooth it down and freeze for about 5 hours.
For the icing, put the chocolate in a bowl. Bring the cream to the boil, pour over the chocolate and stir until the chocolate has melted. Spread the icing on the ice-cream cake and freeze it for at least 2 hours.
To be able to cut pieces with clean edges, the ice must be frozen really solid. Decorate as desired with fresh mint.