Clean and wash the Brussels sprouts. Cook for 15 minutes in boiling salted water, drain. Peel the onions, cut into slices and fry briefly in hot oil. Halve Kabanossi crosswise, cut lengthwise into thin slices.
Pears wash, halve, remove core. Cut pears into thin slices. Layer prepared ingredients in an ovenproof dish. Heat the fat in a pot. Sauté flour in it. Deglaze with stock and milk.
Stir in cheese. Season to taste with salt, pepper and nutmeg. Wash the thyme, pluck the leaves from the stems and add to the sauce. Spread the cheese sauce over the Brussels sprouts. Bake in the preheated oven (electric cooker: 225 ° C/ gas: level 4) for 15 minutes and serve.