Many years ago, my DMIL told me to make a white sauce and add cheese to our liking. Scary...as I'd never done a white sauce, but used Betty Crocker's medium sauce:
For each cup of sauce:
2 Tbsp butter or margarine
2Tbsp flour
1/4 tsp. salt
1/8 tsp. pepper
1 c milk
Melt butter in saucepan over low heat. Blend in dry ingredients until mixture is smooth and bubbly. Remove from hear and stir in milk. Heat to boiling, stirring constantly at boiling temp. for 1 minute.
Hope this helps!