Melt ghee in a large skillet over medium heat. Add onion and garlic; cook and stir until tender, about 3 minutes. Stir in grated cauliflower and cook for 3 minutes. Add mushrooms and cook until tender, about 3 minutes.
Stir Parmesan, cream, salt, pepper, and nutmeg into the skillet; cook over medium heat until creamy, 5 to 7 minutes.
