In a heavy medium sized saucepan, melt the butter over medium heat. Add in the flour and whisk until combined with the butter.
Cook for 2-3 minutes, whisking continuously, until the butter and flour starts to brown and smells nutty.
Slowly pour in the milk whisking continuously as you pour, until the flour mixture has combined with the milk into a smooth mixture. Slowly pour in the beer, whisking, until combined into a smooth mixture again.
Cook for 3-4 minutes, or until mixture has thickened.
Stir in the mustard, Worcestershire sauce, garlic powder, onion powder, parsley, and cayenne.
Add the shredded cheese in to the mixture, a cup or so at a time, whisking it in until it is completely combined.
Remove from the heat, season with salt and pepper to taste, and serve warm.