Wash the potatoes and cook in salted water for about 20 minutes. In the meantime cut the corned beef into pieces. Grate cheese finely. Whisk eggs and cream and season with salt and pepper. Drain potatoes, rinse, peel and slice. Grease a square casserole dish (approx. 22 x 22 cm).
Layer potatoes, corned beef and fried onions. Pour the egg cream over them. Sprinkle with cheese. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: level 2) for approx. 25 minutes until golden brown. Take out and let cool down a little. Garnish with chives and tomatoes