I use this all the time! It's good over pasta or vegetables.
2 Tbsp. butter
2 Tbsp all-purpose flour
1/4 tsp. salt
pepper to taste
1 c. milk (or cream)
Melt butter in a saucepan over low heat. Stir in flour, salt, and pepper. Cook over medium heat, stirring constantly, until mixture is smooth and bubbly; remove from heat. Gradually stir in milk (or cream). Heat to boiling, stirring constantly. Boil and stir 1 minute.
Sometimes I add Parmesan or Gorgonzola...
From Betty Crocker's Cookbook