Debeard the mussels.

Soak the mussels in salted water for 1-2 hours.

Rinse the mussels with cold water.

In a large kettle, heat butter over a low flame.

Add sliced onions, chopped celery, salt, and pepper to the kettle.

Sauté the vegetables until the onions turn yellow, but do not brown them.

Add the mussels atop the onions and celery.

Pour dry white wine into the kettle.

Cover the kettle and heat over a high flame.

Steam the mussels, shaking the kettle every 3-4 minutes, until all shells open wide (about 10 minutes).

Discard any unopened mussels.

Place the mussels into a deep dish or pail.

Ladle some of the remaining liquid onto the mussels.

Top with chopped parsley and serve immediately.