Melt the butter in a saucepan and stir in the flour. Cook for 2 minutes, stirring constantly, then add the dry mustard and stir and cook another minute. (I typically put the milk in the microwave for 2 minutes while I'm doing this as it's easier to make a smooth white sauce if the milk is warmed a bit.)

Gradually add the milk, using a whisk to mix it in so you get a nice smooth sauce. Raise the heat to medium-high and bring to a boil, stirring the whole time so it doesn't scorch. When it's thickened up a bit, reduce the heat to low and add the beer. Simmer for 2-3 minutes, stirring.

Turn the heat way down or off and add the grated cheese a handful at a time, stirring until melted. Stir in the Worcestershire and cayenne.

Toast some English muffins or sourdough bread or whatever you have around and spoon the cheese sauce over the top, sprinkling with paprika.