Peel the potatoes and cook them in salted water (or use the leftover potatoes from the day before), remove the stems from the Brussels sprouts (if fresher is used), cut very large florets at the bottom so that they cook better. Cook in boiling salted water for 10 minutes (if you use frozen Brussels sprouts, cook 2 minutes longer).
While the Brussels sprouts are cooking, prepare the bechamel sauce. To do this, sauté a chopped onion in a little butter or oil, then dust with a heaping spoon of flour, stir and pour the cream and milk over it.
Add the spices (or just some granular broth), bring to the boil. It must have a consistency like cream pudding, if necessary, stir in a little flour with a little milk and add.
Now cut the boiled potatoes into slices, mix with the boiled Brussels sprouts, place in a baking dish and pour the bechamel sauce over them. Bake in the preheated oven at 200 ° C (top / bottom heat) for 30 minutes, if the gratin turns too brown, cover with aluminum foil.
Goes well with hearty meat dishes or schnitzel, then the amount is enough as a side dish for 4 people. As a main meal, it is enough for 2 people.