1/4 cup grated Parmesan cheese, plus more for serving
Preheat the oven to 375 degrees. Lightly spray a 2-quart baking dish with olive oil.
Cook the pasta al dente according to the package directions; drain and set aside.
While the pasta is cooking, in large sauté pan or skillet, heat the olive oil over medium heat. Add the onion, garlic and red pepper flakes and cook until it starts to soften.
Add the sausage, breaking it up with a spatula, and continue cooking until the sausage is no longer pink, around 10 minutes.
Stir in the marinara sauce, sour cream and Cheddar cheese, then stir in the penne. Spoon into the prepared dish and sprinkle the Parmesan cheese over the top. Bake for 15 to 20 minutes or until bubbly and hot.
Serve with additional Parmesan cheese on the side.
Make ahead: Dish can be prepared but not baked earlier in the day, covered and refrigerated. Bring to room temperature before baking.