Melt butter in a medium saucepan over medium-low to medium heat.
Add cream and bring to a light simmer, stirring often for 5 minutes until it starts to thicken slightly.
Add garlic and cook for 1 more minute.
Gradually add Parmesan in batches, whisking constantly until smooth and melted.
Season with salt, pepper, and optional nutmeg to taste.
If the sauce thickens too much, thin with a splash of extra cream or reserved pasta water.
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