Buttermilk White Sauce

Measure out the flour, as for baking, lightly pour it with a spoon into a measuring cup and smooth it out with the back of a knife. This will help you avoid forming a thick, pasty sauce. Do not try to add milk and buttermilk at the same time - the sauce will curdle.
Melt the butter in a heavy medium saucepan over medium-high heat; beat with the flour until smooth. Cook for 1 minute, whisking constantly. Gradually whisk in 1 1/2 cups of milk; cook over medium heat, whisking constantly, for 3-4 minutes or until the mixture thickens and begins to bubble. Remove from heat and whisk with buttermilk and other ingredients.Note: The sauce can be prepared two days in advance. Prepare as directed in the recipe; cover and refrigerate in an airtight container. Whisk 2 tablespoons of milk and reheat in the microwave on high power for 1 minute, stirring at 30-second intervals.