Heat oven to 350F.
Bring a large pot of salted water to a boil. Cook pasta for 3 minutes less than the package directions.
Scoop out 1 1/2 cups of the water from the pot and drain the pasta.
While the water is heating, make the sauce.
Put a large skillet on medium high heat, add the sausage, breaking it up as you add to the skillet. Saute the sausage until cooked through and browned. Transfer the sausage to a bowl.
Reduce the heat to low. Add the garlic and stir for 30 seconds.
Add the tomatoes and red pepper flakes. Bring to a boil, then reduce the heat to a simmer. Simmer for 10 minutes.
Take the sauce off the heat. Stir in the heavy cream, parmesan cheese, and basil. Taste the sauce and add salt, pepper, and/or red pepper flakes as needed.
Now add back in the sausage along with the parboiled pasta and 1 cup of the pasta water. Stir to combine. Add more water if the mix seems dry.
Transfer the mixture to a casserole dish. (13x9 or similar)
Cover the dish with foil and bake for 15 minutes.
Take the casserole out of the oven. Top with the mozzarella cheese. Cover the dish and put it back in the oven for 2 minutes. (Just enough to start softening the cheese.)
Then take the casserole out and let it sit for 10 minutes covered to fully melt the cheese.
Uncover, top with more the basil, and serve.