Mince the onions finely, and saute in a large pan in half the butter.
Trim and clean the mushrooms.
Chop the mushrooms finely.
Cook the onions till they soften, and start to brown. Add the finely minced garlic.
Add half the minced mushrooms and saute over medium high heat to cook off any moisture released by the mushrooms. Add the remaining butter and when melted, add the remaining mushrooms. Continue to cook till the mushrooms are done, and all the liquid has evaporated
Add the cognac (or brandy) and flame. Be careful.
Remove the mussels from their shells. Be careful to remove any broken slivers. Reserve the shells.
Mince the mussel meat.
Add the mussels to the pan, and saute till the moisture is evaporated.
Add the imitation crab.
Break up the pieces of imitation crab and stir in the heavy cream. Adjust seasoning with salt and pepper.
Use this filling to stuff the shells, and then sprinkle with bread crumbs and paprika. Bake at 350 for about 15 minutes or till hot.