Melt the butter in a large saucepan over medium heat. Add the onion, celery and garlic and cook,
stirring occasionally, for about 5 minutes, or until the onion is softened but not browned.
Add the wine, bay leaf and thyme to the saucepan and bring to the boil. Add the mussels, cover
the pan tightly and simmer over low heat for 2-3 minutes, shaking the pan occasionally. Using tongs
or a slotted spoon, lift out the mussels as they open and put them into a warm dish. Discard any
mussels that haven't opened after 3 minutes.
Strain the cooking liquid through a muslin-lined fine sieve into a clean saucepan to remove any
grit or sand. Bring the liquid to the boil and boil for 2 minutes. Add the evaporated milk and
reheat without boiling. Season well. Serve the mussels in individual bowls with the liquid poured
over. Sprinkle with the parsley and serve with bread.