Preheat the oven the 375. Cook bacon according to package directions until crispy. Chop into 1-inch pieces and set aside.
In a large cast iron skillet over medium heat, melt butter. Add shallots and let simmer for 1-2 minutes. Add brussel sprouts and season with red pepper flakes, salt, and pepper. Stir and cook until tender, about 10 minutes.
Remove from heat and pour in heavy cream. Top with both cheeses and bacon.
Put the skillet into a preheated oven and bake for 12 minutes. Cheese should be bubbling.
Remove from the oven and let it stand for 5 minutes. Serve hot.
