Clean the Brussels sprouts and pre-cook them in lightly salted water for about 5 minutes.
Drain and drain well and steam.
Heat a frying pan and fry the bacon in it. Add the chopped onion and fry until translucent. Add garlic and the drained Brussels sprouts and fry briefly.
Stir the creme fraiche through the sprouts and about 75 grams of the grated cheese. Season with salt and pepper if necessary.
Transfer the Brussels sprouts to an oven dish and sprinkle with the rest of the grated cheese. Spread a few knobs of butter on top and gratinate in the oven for about 20 minutes or until the cheese is melted and golden brown.