Prepare the mussels.
Place the herbs, white wine and shallots in a large saucepan and bring to the boil. When boiling, add the mussels, cover with a tightly-fitting lid and cook over a high heat until all the mussels have opened (discard any that remain closed). When ready, remove the mussels from the liquor and discard one half of each shell. Pass the liquor through muslin or a very fine strainer and bring back to the boil. Add the cream, turn down the heat to low and gradually whisk in the butter until it has all melted.