Bring 750 ml water and 1 teaspoon of salt to the boil, remove from the heat. Pour in milk, stir in puree flakes. Pour into a large piping bag with star spout. Pour as tuffs onto the rim of a casserole dish.
Drain the sauerkraut. Heat oil and fry sauerkraut for about 5 minutes. Season with salt and pepper. Pour into the casserole dish. Clean, wash and chop the spring onions. Dice meat loaf.
Wash the apple, quarter it and remove the core. Dice flesh. Heat butter. Fry the meat loaf, apple cubes and spring onions briefly. Season with salt and pepper. Deglaze with stock and cream, bring to the boil.
Stir in mustard and sauce thickener, bring to the boil again, season if necessary. Pour into the casserole dish onto the sauerkraut. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for approx. 15 minutes.