Peel the bananas and cut them in half lengthwise. Put them in an ovenproof dish and sprinkle with the juice of 1 1/2 lemons and honey. Separate the eggs. Beat the egg yolks and vanilla sugar until creamy. Beat the egg whites until very stiff, gradually adding 100 g sugar.
Carefully fold the beaten egg white into the egg yolk mixture. Sift the flour over it and fold in with the muesli. Spread the mixture loosely on the bananas. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for 20-25 minutes.
Mix quark, yoghurt, 50 g sugar, juice of 1/2 lemon and lemon peel. Dust the casserole with icing sugar and decorate with mint. Serve immediately with the quark cream.