Bring 2 liters of water to a boil in a large pot. Add 1 tsp salt and penne pasta. Cook until al dente, about 10–12 minutes. Drain and reserve ½ cup pasta water.

In a medium saucepan over medium heat, melt 4 tbsp butter. Add minced garlic and sauté for 1 minute.

Stir in 3 tbsp flour and cook for 1–2 minutes, whisking constantly.

Gradually add warm milk while whisking. Cook until sauce thickens, about 5–7 minutes.

Stir in 1 cup grated parmesan cheese. Season with salt, pepper, and nutmeg if desired.

Add cooked penne to the sauce and toss until fully coated. Adjust consistency with reserved pasta water if needed.

Serve immediately, garnished with chopped parsley and extra parmesan cheese.