Knead the marzipan, nuts and 3 tbsp. calvados. Wash the apples, grate them dry and cut off one lid each. Prick the core out of the apples. Sprinkle all cut surfaces of the apples with lemon juice.
Press the marzipan mixture into the apples. Spread the rest of the marzipan mixture on top. Press the apple lid on top. Put apples into 2 small ovenproof moulds or 1 large mould.
Separate eggs. Beat the egg whites until stiff, while pouring in 1 heaped tablespoon of sugar. Beat the egg yolks, 4 tbsp. Calvados and 75 g sugar until fluffy. Fold in milk and flour. Carefully fold in the beaten egg white.
Spread the Calvados mixture around the apples. Bake in the preheated oven (electric oven: 175 °C/circulating air: 150 °C/gas: level 2) for 25-30 minutes. Serve the baked apple clafoutis hot.