Drain the cherries and collect the juice. Mix the starch with 100 ml of juice until smooth. Bring the rest of the juice to the boil, remove from the heat and stir in the starch. Simmer for about 1 minute while stirring.
Stir in the cherries and set aside. Mix pudding powder and 50 g sugar, stir with 100 ml milk until smooth. Bring 650 ml milk to the boil, remove from the heat, stir in the pudding powder. Simmer for about 1 minute while stirring.
Leave to cool for about 10 minutes, stirring from time to time to prevent skin formation. Separate the eggs. Beat the egg whites until stiff, pour in 25 g sugar. Stir the egg yolks one after the other into the pudding.
Loosely fold in the egg white. Grease an ovenproof dish (approx. 1 litre capacity). Spread about 1/3 of the pudding mass, 5 rusks and half of the cherries in it one after the other. Place 1/3 of the custard, 5 rusks and the remaining cherries on top.
Cover with remaining pudding. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas. Level 2) for approx. 30 minutes. Crumble 1 rusk roughly. Caramelise 25 g sugar in a pan until golden, mix with rusk crumbs.
Put it on a lightly oiled piece of aluminium foil and let it cool down. Serve the casserole decorated with caramel rusks and mint.