Difficulty: Easy - for beginners
2 tablespoons butter
2 tablespoons flour
1 cup milk
1/2 teaspoon salt
1 cup shredded Gruyere, jack or cheddar cheese
Melt butter in pan and stir in the flour. Remove from heat. Add milk, stirring mixture until it is thickened. Add salt, pepper, and cheese, and mix until cheese is melted into sauce.