Cook the pasta in plenty of boiling salted water for 8-10 minutes. Cook Brussels sprouts in little boiling salted water for about 5 minutes and drain well. Cut corned beef into large pieces. Peel onions and cut them into thin slices.
Drain the pasta. Heat the oil in a coated pan. Fry the onions in it until transparent. Add corned beef and fry. For the sauce, bring milk and 100 ml water to the boil. Stir in the sauce powder. Season to taste with pepper, nutmeg and paprika.
Layer the ingredients in the greased form. Pour sauce over it. Cut cheese into small flakes and place on top. Bake in the preheated oven (electric: 200 °C/ gas: level 3) for 25-30 minutes.