2 tablespoons butter
2 tablespoons flour
1/3 cup milk
1/2 cup beer – I use porter, but you can use anything dark and flavourful
2 teaspoons dry mustard
1/2 teaspoon paprika
1/4 teaspoon cayenne
1 tablespoon Worcestershire sauce
1-1/2 cup extra sharp Cheddar cheese, grated
Melt butter in a saucepan over low heat. Add flour and whisk together until combined. Cook over low heat about one minute, until a nutty brown colour. Pour in milk and beer, whisking constantly, and cook for an additional minute or until it starts to thicken. Add mustard, paprika, and cayenne and whisk. Add cheese and whisk slowly, cooking for a couple of minutes or until smooth, melted, and very hot. Serve immediately over toast.
I never met a cheese sauce I didn't like.