Preheat oven (electric cooker: 200 °C/circulating air: 175 °C/gas: see manufacturer). Heat oil in a large pan. Fry the Maultaschen for 5-7 minutes while turning.
In the meantime whisk milk and eggs, season with salt, pepper and 1 teaspoon marjoram. Grease casserole dish. Roughly pluck the ham. Cut Maultaschen into thick strips. Mix with frozen peas and ham and fill into the dish.
Pour egg milk over it, sprinkle with cheese. Bake in a hot oven for about 15 minutes until golden brown.