Bechamel sauce

   4   tbsp unsalted butter
   3   tbsp unbleached flour
 1 1/2 cups milk
       pinch paprika
       pinch ground nutmeg
       salt and ground white pepper, to taste

melt butter in heavy sauce pan; add flour; stir 3 minutes over low
heat; raise heat to medium; add milk; stir constantly

whisk 5 minutes until sauce thickens; add paprika, nutmeg, salt,
pepper; stir

source: New Basics (needed for their lasagna)