Heat half the butter in a large heavy-bottomed pan and add the shallots, garlic, bay leaf and picked thyme leaves.
Soften for five minutes without colouring then pour in the wine and bring up to the boil. Simmer for a further five minutes before turning up the heat to high.
Tip the mussels into the pan and cover with a tight-fitting lid. Steam for three minutes until the mussels have all started to open and remove from the heat.
Add the remaining butter and the parsley, replace the lid and put back on the heat for thirty seconds shaking the pan well to distribute the parsley.
Season with freshly ground black pepper and serve immediately, removing any mussels which have remained closed.