Peel and wash the potatoes and cut them into thin slices. Cut garlic in half. Spread 2 smaller gratin dishes with garlic, grease and layer potatoes in flakes. Stir starch with 3 tablespoons of milk until smooth.
Mix cream, remaining milk and mixed starch, season with salt, pepper and nutmeg and pour over the potatoes. Wash the marjoram, dab dry, remove coarse stalks. Coarsely chop leaves. Cut cheese horizontally into 4 slices and place on the gratin.
Sprinkle with marjoram. Cook in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for approx. 45 minutes. In the meantime wash and drain the spinach. Clean and wash the peppers, dab dry and cut into small cubes.
Peel and finely chop the onion. Heat 1 tablespoon of oil in a pan. Add the spinach, peppers, 2 tablespoons of water and diced onion to the pan and sauté for approx. 3 minutes while tossing until the spinach collapses completely.
Season spinach with salt and pepper, remove and drain thoroughly. Rinse fish and pat dry. Place fish fillets on 1 slice of ham each, season with pepper and a little salt.
Spread the spinach mixture over the fillets. Roll up the fish with the ham and fix with toothpicks. Heat 1 tablespoon of oil in a pan. Fry the fish rolls for 8-10 minutes until golden brown.
Arrange fish and gratin on preheated plates, garnish with lemon wedge.