Cook Pasta: Boil penne pasta until al dente, drain, and set aside.
Brown Sausage: In a large skillet, heat olive oil over medium heat, add Italian sausage, and cook until browned, breaking it up with a spoon (5-7 minutes).
Add Garlic: Stir in minced garlic and cook for about a minute until fragrant.
Add Spinach: Add spinach to the skillet, cooking until wilted (about 2-3 minutes).
Make Sauce: Pour in heavy cream, stirring to combine, then gradually add Parmesan until the sauce is melted and creamy.
Season and Combine: Season with salt, pepper, and red pepper flakes if desired, then add cooked pasta and mix to coat.
Serve: Serve warm, garnishing with extra Parmesan if desired.