Melt butter in a medium saucepan over medium heat. Add minced garlic and saute for about 30 seconds, until fragrant.
Add the heavy cream. Bring to a gentle simmer, then continue to simmer for about 5 minutes, until it begins to thicken and volume is reduced by about ⅓. (Amount of time will vary depending on the size of your saucepan.)
Reduce heat to low. Gradually whisk in the Parmesan cheese. Keep whisking over low heat, until smooth.
Stir in nutmeg, sea salt, and black pepper, to taste. If sauce is thicker than you like, you can thin it out with more cream.