Wash the potatoes and cook in plenty of boiling water for about 20 minutes. Drain, rinse with cold water, drain and peel. Drain the peppers and let them drain. Cut tomatoes and peppers into cubes.
Clean, wash and cut the spring onions into rings. Whisk crème fraîche, milk and eggs. Stir in cheese. Season with salt and pepper. Cut ham into cubes. Cut potatoes into slices.
Carefully mix all ingredients except for a few spring onion rings for garnishing and place in a greased casserole dish. Bake in a preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for approx. 1 1/4 hours.
Cover with foil after 30 minutes. Sprinkle the finished potatoes with the remaining spring onions.