Melt butter over medium heat in a small saucepan. Do not let the butter brown! Once melted, add flour and cook, stirring continuously until the mixture is incorporated and lightly golden. Once again, do not let butter/flour mixture start to brown.

While stirring the butter/flour mixture, slowly pour in milk. Stir over medium heat until the roux is thick and bubbly. It can take 3- 5 minutes for the mixture thicken depending on your stove and pot. Once you see bubbles, remove from heat and stir in cheese. Stir until cheese is blended and your sauce is ready.