In a large pot, bring salted water to a boil and cook the pasta according to the package instructions. Drain and set aside.
In a large skillet or saucepan, melt the butter over medium heat. Once the butter is melted, add the minced garlic and sauté for about 1 minute until fragrant.
Add the flour and stir constantly for 1-2 minutes to create a roux. This will help thicken the sauce.
Slowly pour in the milk or cream, whisking constantly to avoid lumps. Bring the mixture to a simmer and cook for 5-7 minutes, until it thickens.
Add the Parmesan cheese and stir until the cheese melts and the sauce becomes smooth. Season with salt and pepper to taste.
Add the cooked pasta to the sauce and toss to coat the pasta evenly with the creamy sauce. If you're adding chicken, spinach, or mushrooms, stir them in now.
Serve the white sauce pasta hot, with extra Parmesan cheese sprinkled on top if desired. Enjoy with your favorite side dishes.