Cook the chopped bacon over medium heat until crispy, about 8 minutes. Remove the bacon, but leave 2 tablespoons of grease in the pan.
Turn the heat to medium-high. Place the Brussels sprouts cut-side down and sear for 5-6 minutes until browned.
Flip them over and cook another 3-4 minutes to brown the other side.
Add the garlic and cook for 30 seconds until fragrant.
Pour in the cream and cream cheese. Stir until smooth and creamy, about 2 minutes.
Mix in the parmesan, butter, and most of the bacon. Season with salt, pepper, thyme, and red pepper flakes if using. Simmer for 2-3 minutes until thickened.
Top with the reserved bacon and extra parmesan or red pepper flakes before serving.