Stir the fresh blue mussels in a colander while rinsing in tap water. Set aside for a few minutes. Tap any that are open and discard those that don’t close in response to the tap.
Add 1 tablespoon butter to pot, cook chopped onion and celery, salt and pepper, stirring occasionally, until softened, about 5 minutes.
Add the beer and fresh mussels.
Cover and steam over high heat until the mussels are open (6-8 Minutes).
Squeeze the lemon juice over the mussels, add some parsley and pour into a large bowl to share. Don’t forget to sip the sauce!