Add the butter into a medium saucepan.
When the butter is melted and bubbling add the flour. Whisk until combined.
Gradually add the beer, whisking constantly, until combined. Cook for a minute over low heat.
Add the milk and spices: onion and garlic powder, Worcestershire sauce, mustard, and cayenne. Cook over medium-low heat for a minute, whisking from time to time. Reduce the heat to low.
Add shredded cheese in 2 additions, whisking after each addition until the cheese is melted.
When all the cheese has been incorporated, season the sauce with salt and pepper to taste.
Leave to cool and thicken (about 5-10 minutes), then enjoy!