Rinse the mussels under cold running water
Scrub the shells and remove any beards
Discard any mussels that are cracked or stay open when tapped
Heat a large pot over medium heat
Add butter or olive oil
Add chopped garlic, onion, or shallot if desired
Pour in a small amount of white wine, broth, or water
Bring the liquid to a simmer
Add the mussels to the pot
Cover with a lid
Cook for 5 to 7 minutes, shaking the pot occasionally
Remove the mussels when the shells open
Discard any mussels that do not open
Serve immediately with the cooking liquid
Add parsley, lemon juice, or pepper if desired