Add the bacon to a large, deep skillet over medium heat and fry, stirring often, until bacon is crispy. Remove bacon with a slotted spoon to a paper towel lined plate to drain.

Drain all but 2 tablespoons of bacon grease from the skillet.

Add the onion to the skillet and cook until softened, about 5 minutes.

Stir in the Brussels sprouts and cook for 5 minutes, stirring often. Stir in the garlic and cook for 1 minute more.

Add the chicken stock to the pan and cover the pan. Cook over low heat for 8 minutes or until Brussels sprouts are tender.

Remove the lid from the pan and add the heavy cream, Parmesan, and salt to the pan. Stir well to combine. 

Let cook over low heat, stirring often, until the sauce has thickened and the cheese has melted, about 3 minutes.

Stir the bacon back into the pot and sprinkle with red pepper flakes before serving.