If you are using mostly clams or mussels, use the larger amount suggested.
Combine in a large heavy saucepan:
Cook, stirring, over medium heat, until the mushrooms begin to soften, about 5 minutes. Add:
Increase the heat and simmer for 5 minutes, or until the greens are tender. Stir in:
Cover the pan, reduce the heat to medium-low, and cook until the shellfish are cooked (or, in the case of whelk or octopus, heated through) and any mussels or clams have opened, 5 to 10 minutes. Season to taste with:
Spoon the shellfish, mushrooms, and greens into serving bowls and pour some of the cooking juices over them. Drizzle with: