In a saucepan over medium heat, add butter and allow it to melt. Mix in flour once melted, and cook for 2-3 minutes, combining with a rubber whisk until it forms a paste-like consistency and is a pale golden color.
3 Tablespoons butter, 3 Tablespoons flour
Gradually add in milk slowly and while stirring. The flour mixture will combine smoothly with the milk. Once it does, season with salt and pepper to taste.
2-3 cups milk, kosher salt and black pepper, to taste
Remove from the heat and add the cheese. Return the saucepan to the stove, turn down the heat to low, and stir constantly until the cheese melts. If the sauce looks too thick, you can add some more milk. Serve, and enjoy!
1 cup grated cheddar or gruyere cheese
Notes
Reheating: Keep cheese sauce in the fridge for up to one week. Reheat on low in the microwave or in a saucepan over medium heat with some additional milk.