In a pot, melt butter over medium heat and sauté garlic until fragrant—about 1 minute.
Pour in cream and milk, then simmer gently for 3–4 minutes to reduce slightly.
Gradually whisk in Gruyère, Parmesan, and mozzarella until smooth and glossy.
Season with salt, pepper, and a pinch of nutmeg if you’re feeling fancy.
Fold in hot pasta directly from the pot, letting the sauce cling to every strand.