Cook bacon in a skillet. Remove and chop. Reserve 1-2 tablespoons of the grease in the pan.
Bring a large pot of water to a boil. Add 1 tablespoon of salt.
Cut off the ends of the Brussel sprouts and cut in half. Add to the boiling water. Cook for 4 minutes. Drain.
Add galic, onion and Brussel sprouts to the pan. Season with salt and pepper to taste (1/2 tsp salt and 1/8 tsp black pepper). Cook for 2 minutes.
Add the heavy cream. Add cheese (gruyere or Parmesan) and bacon. Top with mozzarella.
Preheat oven to 375 F. Bake Brussel sprouts for 20-25 minutes, until the cheese on top is bubbly. Serve.