Gather ingredients: butter, all-purpose flour, milk, shredded cheddar (or cheese of choice), salt, black pepper
Warm a saucepan over medium heat
Melt butter in the saucepan
Whisk in flour and cook 1–2 minutes, whisking constantly
Slowly pour in milk while whisking until smooth
Continue cooking and whisking 3–5 minutes until thickened
Reduce heat to low
Add shredded cheese a handful at a time, stirring until melted
Season with salt and black pepper to taste
If too thick, stir in a splash of milk until desired consistency
If too thin, cook on low 1–2 minutes while stirring until thickened