In a saucepan, melt the butter over medium heat.
Add the minced garlic and sauté for about a minute until fragrant.
Stir in the flour to make a roux. Cook for 1-2 minutes, stirring constantly.
Slowly whisk in the milk and heavy cream, ensuring there are no lumps.
Cook the sauce, whisking constantly, until it thickens, about 5-7 minutes.
Add the grated cheddar cheese and continue to stir until the cheese is fully melted and the sauce is smooth.
Season the sauce with salt, pepper, and nutmeg (if using). Adjust the seasoning to taste.