In a large skillet or saucepan, melt the butter over medium heat. Once melted, add the minced garlic and sauté for about 1 minute, until fragrant but not browned.
Pour in the heavy cream and bring the mixture to a gentle simmer. Stir occasionally and let it cook for 5 minutes, allowing the cream to slightly thicken.
Lower the heat to medium-low and gradually whisk in the Parmesan cheese, about 1/2 cup at a time. Stir until the cheese melts completely before adding more. The sauce should become smooth and creamy.
Season with salt, pepper, and nutmeg if using. Taste and adjust as needed.
If the sauce feels too thick, add a splash of reserved pasta water or a little extra cream to loosen it. If too thin, let it simmer for another 2–3 minutes to reduce.
Remove from heat and toss immediately with cooked pasta or drizzle over your favorite main dish. Garnish with fresh parsley before serving.