Here is the recipe that you are looking for:
Basic white sauce turned cheese sauce:
1/2 stick of butter (4 tablespoons)
1/4 cup flour
1 tsp salt
1/8 teaspoon (or a big pinch) pepper
1 1/2 cups whole milk (do not cheat and used reduced fat or skim or your sauce will taste like a combination of dog poo and wallpaper paste-you have been warned)
1/2 cup heavy cream (we all have to cheat now and again)
one golf ball size portion of Parmesan cheese, finely grated (no cheating and using the stuff in the little green can. Call me if you need a reasonably priced recommendation)
1. Combine flour, salt & pepper in a bowl and set aside.
2. Melt butter over medium heat, stirring constantly. When butter is melted remove pan from heat.
3. Gradually add flour mixture and stir until smooth.
4. Combine the whole milk and heavy cream in a liquid measuring cup with a spout. Slowly whisk into the butter and flour mixture.
5. Place back onto burner over medium heat and whisk constantly until boiling. Boil for two minutes.
6. Remove from heat. Grate in Parmesan cheese and stir until melted.
7. Pat yourself on the back, you have just made a white sauce and then a cheese sauce. You also made a roux (combining the butter and flour and cooking the flour- although we used the heat of the pan to cook it), which is the basis for soups and other yummy goodness.