Step 1: Melt the Butter - In a medium saucepan over medium heat, melt the 3 tablespoons of unsalted butter. Allow it to foam and bubble, but be careful not to let it brown.
Step 2: Whisk in the Flour - Once the butter is melted, add the 3 tablespoons of all-purpose flour. Whisk constantly for about 1-2 minutes until the mixture is smooth and slightly golden. This is called a roux.
Step 3: Gradually Add the Milk - Slowly pour in the 2 cups of milk, whisking continuously to prevent lumps from forming. This is crucial for achieving that silky texture.
Step 4: Thicken the Sauce - Continue to whisk and cook the sauce over medium heat until it thickens and starts to bubble. This should take about 5-7 minutes.
Step 5: Season the Sauce - Once thickened, add 1/4 teaspoon of nutmeg and salt to taste. Stir well to combine, and remove from heat.
Step 6: Use or Store - Your Bechamel sauce is now ready to be used in your favorite recipes!