Melt 2 TBS butter on medium heat in large frying pan. Add chopped onions and garlic and cook until just translucent. Pour in wine with pan removed from stove to prevent flare-up. Add a scant handful of chopped parsley, retaining half for garnish. Add pepper flakes, salt and pepper to taste. Mussels are salty so you probably won’t need to add any salt. Cook the sauce until the wine reduces by half. Add the remaining butter to help thicken the sauce slightly. If it doesn’t look buttery enough, add some more. Mussels love butter! This would be a good time to cook your pasta. With the white wine sauce simmering, place the drained mussels into the pan and stir as the shells open. Continue cooking the mussels for about 5 minutes. Do not overcook or they will be rubbery. Discard any that do not open.