Preheat oven to 375F

Place the brussels sprouts in a large bowl and cover with warm water. Allow to sit for 10-15 minutes. Drain and set aside

I a large, deep pan cook bacon til crispy, 8-10 minutes. Remove from pan and drain most of the grease.

Add the brussels sprouts to the pan, stirring to coat in the grease. Saute covered about 12 minutes, stirring occasionally until outer leaves begin to caramelize. Stir in garlic and onions and continue to saute til onions soften.

Pour brussels sprouts into a 13x9 baking dish, evenly spread the bacon over them, then evenly add the cheddar. Pour over the cream, then top evenly with the gruyere.

Bake at 375F for 15 minutes.