This dish is based on classic moules mariniere, with a bit of cream added.
Heat oil in a large pot over medium heat. Add shallots; cook, stirring, until translucent, about 3 minutes. Add saffron, if desired, and wine; bring to a boil. Add mussels; cover and cook, stirring once, until mussels open, about 3 minutes. (Discard unopened shells.)
Remove mussels with a slotted spoon. Transfer to a bowl; cover. Strain cooking liquid; discard solids. Return liquid to pot; bring to a boil. Add cream; reduce to a simmer; cook until slightly thickened, about 3 minutes. Divide mussels among 4 bowls. Add sauce; serve.