Preheat oven broiler.

Cook pasta according to package directions until al dente; drain well.

While pasta cooks, melt butter in a large skillet over medium heat.

Add minced garlic to the melted butter and cook until fragrant, about 1-2 minutes.

Stir in flour to create a roux.

Gradually whisk in chicken broth until the mixture is smooth and free of lumps.

Stir in half and half.

Add salt, pepper, cayenne pepper, and red pepper flakes to the sauce.

Simmer the sauce until it has thickened, approximately 5 minutes, stirring occasionally.

Stir in Parmesan cheese and 1 cup of mozzarella cheese until the cheeses are fully melted and the sauce is smooth.

Slice the smoked sausage into 1/4 inch thick pieces.

Add sliced sausage, chopped fresh parsley, and cooked pasta to the sauce.

Season with additional salt and pepper to taste, if needed.

Pour the pasta mixture into a lightly greased 9x13 inch baking dish.

Top the pasta with the remaining mozzarella cheese.

Broil in the preheated broiler for 2-3 minutes, or until the cheese is bubbly and golden brown.