Clean the mussels: Rinse under cold water. Scrub the shells and remove beards. Discard any open or broken ones.
Sauté aromatics: Warm olive oil in a big pot over medium heat to start cooking the aromatics. Add garlic and shallots. Cook for 1–2 minutes until soft.
Add mussels: Stir in the mussels. Pour in white wine. Cover with a lid.
Steam mussels: Cook for 5–7 minutes until mussels open. Shake the pot gently once or twice during cooking.
Finish: Remove from heat. Add butter, lemon juice, salt, pepper, and parsley. Stir gently.
Serve hot: Spoon mussels into bowls. Pour broth over top. Serve with bread or fries.