1. Bring a large pot of salted water to a boil. Cook the pasta according to the package directions until tender. Drain well and set aside.

2. While the pasta cooks, heat a large pot over medium heat. Add the turkey sausage and cook for 5–7 minutes, breaking it into small pieces as it browns. Once fully cooked, transfer the sausage to a plate.

3. In the same pot, melt the butter over medium heat. Add the diced onion and cook until softened, about 3 minutes. Stir in the garlic and cook for another 30 seconds.

4. Sprinkle the flour over the onion mixture and stir continuously for 1 minute to create a roux.

5. Slowly pour in the milk while whisking to keep the sauce smooth. Add the Italian seasoning, black pepper, and dry mustard.

6. Continue cooking over medium heat, stirring often, until the sauce thickens to a creamy consistency, about 8–10 minutes.

7. Reduce the heat to low and gradually stir in the cheddar, mozzarella, and Gruyère cheese until fully melted and smooth. Taste and add salt if needed.

8. Return the cooked sausage and drained pasta to the pot. Stir everything together until evenly coated in the cheese sauce.

9. Serve hot and enjoy.