1. Start by bringing a large pot of salted water to a boil. Add the elbow macaroni or pasta shells and cook until al dente, following the package instructions. Drain the pasta and set it aside.

2. In a large skillet, melt the unsalted butter over medium heat. Once the butter is melted, whisk in the all-purpose flour and cook for about 1 minute, stirring constantly.

3. Slowly pour in the milk, whisking continuously to prevent any lumps from forming. Allow the mixture to cook, stirring occasionally, until it begins to thicken.

4. Add the shredded cheddar and mozzarella cheeses to the thickened sauce. Stir until the cheeses are fully melted and the sauce is silky smooth. Season with garlic powder, onion powder, salt, and black pepper to taste.

5. Stir in the browned smoked sausage slices and the cooked pasta. Gently toss everything together until the pasta is evenly coated in the creamy, cheesy goodness.

6. Serve warm, garnished with a sprinkle of fresh chopped parsley, if desired.