Check that all the mussels are tightly closed, wash under cold water and drain. Put into a wide saucepan and cover with a lid or a folded tea-towel. Steam open on a medium heat (this will only take 2–3 minutes). Remove the mussels from the pan just as soon as the shells open, allow to cool, remove the beards and discard the shells. Strain the mussel liquid and reserve.
Put the julienne