Or as those crazy culinary kids call it, bechamel.
From a box sold in San Antonio, Texas.
2 Tablespoons butter
2 Tablespoons flour
1/4 teaspoon salt
1/4 teaspoon pepper
1 cup milk
Melt butter on low heat in heavy pan. Blend in flour–salt–pepper–cook over low heat till smooth and bubbly.
Remove from heat and add milk, stirring constantly. Boil 1 min.