In a medium-sized pan over medium-high heat, add Guinness.

Bring the beer to a boil and reduce heat to a simmer.

Add softened cream cheese and whisk until it is fully incorporated with the beer. A whisk is best here, but you can use a spoon, it just might take a bit more time.

Once the cream cheese is incorporated, add the shredded cheese slowly in batches. Whisk each batch until it is incorporated. Continue adding cheese and continue whisking. 

At this point you might need to let it simmer, stirring regularly for 5 to 10 minutes. You're just looking for everything to start becoming a bit thickened.

Once everything starts thickening add Dijon mustard, Worcestershire sauce, onion powder and cayenne powder (if using). 

Stir everything several times to fully incorporate.

Taste to see if it needs salt and pepper and add if needed. The cheese might be salty enough, but taste just in case. 

Remove to a serving vessel and serve