Remove the outer leaves from the Brussels sprouts, cut the florets in half, rinse and drain. Heat half of the butter and sauté the Brussels sprouts in it.
Peel the potatoes, rinse, dice, add and sauté them. Pour in the broth and cream, season with salt, pepper and nutmeg and simmer gently for about 25 minutes. Stir in the crème fraîche and season to taste. Cut the sausages into slices and heat them in the soup.
Melt the remaining butter and leave the bacon in it. Peel and dice the onions, add and sweat until translucent.
Serve the Brussels sprouts stew and sprinkle with the bacon and onion mixture.