1.
Use dried flap mushrooms. Soak them in warm water for about 20 minutes. Then dice them. Dice the oyster mushrooms, too.
2.
Fry the finely diced onion in butter, add the diced flap mushrooms and oyster mushrooms, salt, pepper, crushed garlic, marjoram and braise while you gradually add the water used for soaking the flap mushrooms. Stir until the water has evaporated. Then remove from fire.
3.
Beat the egg-whites and grate the cheese, then mix them. Add the mushrooms and the sweet corn. Mix well.
4.
With wet hands make walnut-sized balls (be careful because they crumble easily) and pass them through flour, beaten eggs and breadcrumbs. Then fry them in hot oil.
5.
Serve with ketchup.
Variations
For a less strong taste of flap mushroom you can use 20 g of dried flap mushrooms and 130 g of oyster mushrooms.