Rinse mussels under cold running water and scrub shells; remove any barnacles
Discard any mussels that are cracked or won’t close when tapped
Soak mussels in cold water with a pinch of salt for 20–30 minutes (optional), then rinse again
Choose a pot with a tight-fitting lid
Add aromatics to the pot (garlic, shallots, celery, or herbs) with butter or olive oil
Add liquid (white wine, broth, or water) and bring to a simmer
Add mussels in a single layer, cover with a lid
Steam until shells open, about 5–7 minutes (discard any that do not open)
Taste cooking liquid and adjust seasoning with salt, pepper, and lemon juice if desired
Serve immediately with the cooking liquid (for dipping bread) and garnish with parsley
If making ahead, keep opened mussels covered in the cooking liquid and eat within 1–2 hours; reheat gently without boiling