Pour the beer in a medium pan and bring to a simmer.
Lower to medium heat and add the cubed cream cheese.
Use a whisk to stir and work the cream cheese into the beer until it's completely melted. (It's normal for the sauce looks a little broken at this point)
Add the dijon mustard, garlic powder, worcestershire sauce, sriracha and (optional) cayenne pepper
Turn the heat down to low and add the cheese a half-cup at a time, whisking constantly. Allow the cheese to melt before adding the next half-cup. (BE PATIENT! The sauce will go through stages and look like it's not coming together, but just keep whisking it over low heat.)
Continue cooking over medium-low heat about about 4-5 minutes until it is smooth and thick. Do not let it boil once you've added the cheese, or the sauce will break.
When all of the cheese is melted and the sauce is smooth, remove it from the heat and taste for seasoning. I usually add a pinch of salt and a healthy amount of black pepper, but you can add more Sriracha, mustard, or whatever other spices you like.
Serve immediately with green onions sprinkled on top for garnish, if desired.
