Melt the Butter: In a saucepan, melt the unsalted butter over medium heat.

Make a Roux: Once the butter is melted, add the all-purpose flour to the saucepan. Whisk continuously to combine the flour with the butter, forming a smooth paste called a roux. Cook the roux for 1-2 minutes, stirring constantly, until it becomes fragrant and slightly golden in color.

Add the Milk and Cream: Gradually pour the whole milk and heavy cream into the saucepan, whisking constantly to prevent lumps from forming. Continue whisking until the mixture is smooth and well combined.

Simmer the Sauce: Bring the sauce to a gentle simmer over medium heat, stirring frequently. Let it cook for 5-7 minutes, or until it thickens to your desired consistency. The sauce should coat the back of a spoon.

Season with Salt, Pepper, and Nutmeg: Once the sauce has thickened, season it with salt, black pepper, and a pinch of ground nutmeg. Stir well to incorporate the seasonings evenly into the sauce.

Serve: Remove the sauce from the heat and use it immediately in your favorite dishes. Enjoy your creamy and flavorful sauce!