4 tbsp. (1/2 stick) butter
4 tbsp. all-purpose flour
2 cups hot milk
salt and pepper to taste

Melt butter in heavy-bottomed saucepan. Add flour and cook, stirring constantly, until mixture becomes a thick bubbly paste, but do not let it brown. Add milk, stirring constantly as sauce thickens. Bring to a low boil and season with salt and pepper. Simmer for 2 to 3 minutes more, again stirring constantly.