How to Make It
In a large saucepan, combine the beans, carrot, celery, onion, bay leaf and thyme with enough water to cover by 1 inch. Bring to a boil. Cook over moderate heat until the beans are tender and creamy, about 20 minutes. Drain the beans and discard the vegetables and herbs.
In a large skillet, heat 3 tablespoons of the olive oil until shimmering. Add the chorizo, shallots and garlic and cook over moderate heat, stirring, until the chorizo fat starts to render and the shallots have softened, about 2 minutes. Add the clams and cook, stirring, until just warmed through, about 2 minutes. Stir in the beans, vinegar and paprika and cook until the beans are hot, about 2 minutes. Remove from the heat and stir in the parsley and 2 tablespoons of water. Season with salt and pepper and keep warm.
In a very large skillet, heat the remaining 2 tablespoons of olive oil until shimmering. Season the scallops with salt and pepper, add them to the skillet and cook over moderately high heat until browned on the bottom, about 2 minutes. Turn the scallops over and cook until opaque, about 2 minutes longer. Transfer the scallops to a plate to stop the cooking.
Spoon the cranberry beans and clams onto plates and arrange the scallops and watercress on top. Drizzle with olive oil and serve right away.