Cheese Sauce:
Do not use milk. Thats where you are goin wrong.
Use this:
Melt a cube of butter in a sauce pan. Put 2 cups water in a measuring cup and add about 2-3 teaspoons Wondra flour. Once the butter is melted, add the water and flour combo to the butter. Whisk rapidly until it starts to boil. Add in 2 cups cheddar or whatever kind of cheese you want. Stir until melted.
You can adapt this sauce to be really cheesy and spicy for Nachos or Cheese fries, or you can use as is in scalloped potatoes or broc and cheese, etc.