Basic Mornay sauce

1/2 c butter
3/4 c pl. flour
4-5 cups warmed milk
1/4 teaspoon salt
1/4 teaspoon white pepper
pinch freshly grated nutmeg (optional)
1/2 c grated tasty cheese

In a medium saucepan melt the butter over medium heat. Add the flour and cook, stirring constantly, until the roux is pale yellow and frothy, about 1 minute. Do not allow it to brown. Slowly whisk in 4 c milk and continue to whisk until the sauce thickens. Add the remaining milk, bit by bit until desired consistency. Reduce the heat to a simmer and season with the salt, pepper and nutmeg. Allow to simmer for 2 to 3 minutes. This is now called a bechamel sauce, and may be used as is to top any number of dishes.
Stir in the cheese and whisk until melted. Once the cheese is added it is called a mornay sauce.

I use this as a sauce with Tuna and corn in Tuna Mornay, aswell as to fill vol-au-vent cases with either Tuna, chicken or vegetables. I add less milk for a thicker consistency when filling vol-au-vents. The sauce can be used in Lasagne too, layered between the meat sauce.