Pour milk into a saucepan.

Add butter, flour, salt, and pepper to the saucepan.

Place the pan over medium heat.

Whisk constantly until the butter melts.

Incorporate all the flour by working the whisk into the edges of the pan.

Whisk frequently until the mixture comes to a boil.

Reduce heat to low and simmer for about 5 minutes, stirring occasionally, until the sauce reaches the desired consistency.

Taste and add extra seasoning if required.

For Mustard Sauce Variation: Use 1 1/2 cups milk and 1/2 cup chicken stock.

Add 2 teaspoons mustard powder, 1/4 teaspoon onion powder, and a pinch of cayenne pepper instead of black pepper.

Stir in 1 teaspoon lemon juice when the sauce is completed.

For Cheese Sauce Variation: Use 1 cup milk and 1 cup cream.

Add a pinch of nutmeg and cayenne pepper instead of black pepper.

At the simmering stage, stir in 75g-100g grated cheese.

Stir in 1 teaspoon lemon juice when the sauce is completed.

For Parsley Sauce Variation: Use 1 3/4 cups milk and 1/4 cup cream.

When the sauce is finished, mix in 4 tablespoons finely chopped parsley and 1 teaspoon lemon juice.