To ensure that the finished dish is free from sand and dirt, wash the mussels very thoroughly before cooking. This can be done under running water using a brush. Carefully check the mussels for cleanliness and freshness. If using frozen mussels, defrost them first and drain off any excess liquid.
Prepare mussels and vegetables. Rinse the mussels under running water. Peel the onions and garlic and rinse. Cut the onion into small cubes, chop the garlic with a knife or pass through a press. Finely chop the parsley.
Fry the vegetables. In a frying pan over medium heat, heat the butter and olive oil, add the chopped onion and garlic and fry for 3-5 minutes until the vegetables soften. Then add bay leaf, pour in dry white wine and mix well.
Fry the mussels. Turn up the heat under the frying pan, add mussels and dry Provençal herbs to the vegetables and white wine. Stir, close the lid and leave for 5-6 minutes. After this time, open the lid, pour cream into the pan, add chopped parsley, salt and ground black pepper. Reduce heat to medium, close the lid and leave for another 3-4 minutes.
Serve the mussels in the creamy sauce with a side dish of cooked rice and sprinkle the mussels with finely chopped green onions. A glass of light dry white wine also goes well with this dish.