Prepare the ingredients before starting to cook because this is a fast recipe and you will want to have the ingredients next to you. Measure ingredients and slice cheese.
Melt butter over medium heat and whisk in flour until smooth.
Start pouring in beer while slowly whisking. Let the mixture come to a simmer.
Add cheeses, milk, mustard, and seasonings.
Slowly stir with a whisk or a wooden spoon while the cheese is melting.
Once cheese is melted, let it come to simmer and take it off heat.