Melt butter in saucepan over medium heat, add 2-tablespoons flour and cook until frothy (don’t brown). Whisk in warm milk. Continue to stir and cook until and starts to bubbly. Remove from heat, add seasonings to taste (this is a bechamel or white sauce). Add cheese and stir until melted (now it’s a Mornay sauce). Sauce will thicken as it cools. If a thicker sauce is prefered, use 3-tablespoons flour (or more).