Melt the butter in a pan over medium heat, adding the sage leaves as it melts.
Cook until the butter begins to darken and develop a nutty aroma, about 3-4 minutes.
Stir in the minced garlic and cook for 1-2 minutes, or until fragrant.
Reduce heat to low, then stir in the heavy cream, Parmesan cheese, salt, black pepper, and nutmeg.
Cook, stirring frequently, until the sauce thickens and becomes bubbly, about 3-5 minutes.
Remove from heat and serve immediately over butternut squash ravioli.