In a wide skillet with a lid, melt
butter over medium-high heat. Add
onion and
shallot, and stir until very soft and beginning to turn gold, about 5 minutes; do not let them
brown. Add
thyme and bay leaf and stir. Add
wine and 1 cup water and bring to a boil over high heat. Add
mussels, cover, and
cook until open, about 4 minutes.