2 tablespoons butter
2 tablespoons flour
1/4 teaspoon salt (optional)
1 cup milk
1/2 to 1 cup shredded cheddar cheese
In a heavy saucepan, melt the butter. Sprinkle the flour over it and stir to incorporate. Cook over medium-low heat for 2-3 minutes, stirring constantly. Slowly whisk in milk. Add cheese and stir until melted.