Cook pasta in salted boiling water according to package instructions. Reserve 1/2 cup of pasta water before draining.
In a large skillet over medium heat, melt butter and add sausage slices. Cook until browned on all sides, about 6–8 minutes.
Add garlic, Italian seasoning, and red pepper flakes. Sauté for 1–2 minutes until fragrant.
Pour in heavy cream and reserved pasta water. Stir to combine, then reduce heat and simmer for 3–4 minutes.
Add Parmesan cheese and cooked pasta. Toss everything together until the pasta is coated and creamy.
Season with salt and pepper to taste. Garnish with chopped parsley before serving.