Preheat oven to 175 degrees. Peel potatoes, wash, cut into cubes. Peel parsley roots, divide into small pieces. Peel garlic and chop finely. Cook potatoes in salted water for about 15 minutes, add parsley roots and garlic after 5 minutes.
Then drain water, add 200 ml milk and 1 tablespoon butter to the vegetables in the pot. Mash in pieces and spread in a large, greased casserole dish.
Meanwhile, wash and clean cabbage, divide into small florets. Heat 1 tablespoon each of butter and oil in a deep skillet, sauté cabbage in it for about 10 minutes over medium heat, stirring until al dente, and add to potato mixture. Mix remaining milk with eggs and mustard, season with salt, pepper, nutmeg. Wash parsley, shake dry, pluck leaves, chop finely.
Stir into egg mixture with cheese. Pour egg mixture over cauliflower. Spread bacon slices on top.
Bake casserole at 175 degrees for about 40 minutes.