Cut the leeks and mangetout in julienne(thin strips) and fry them in some oil. Season well salt and pepper until the leeks become transperant. Remove from heat and add the fresh mint. Chop the onion and garlic and cook on low heat for a minute or two before adding in the white wine. Bring to the boil then add the fish stock, bayleaf and the juice of half thelemon and simmer for a few minutes. Meanwhile, cut the butter in small cubes add to the sauce along with the cream and whisk well until the butter has melted. Seasoned the scallops well with salt and pepper and quickly pan-fry lightly in a hot pan drizzled with a drop ofolive. Squeeze over the juice from the remaining lemon and flip the scallops over onto their opposite side. Continue to cook for a minute then quickly serve onto 2 plates drizzled with the creamy butter sauce. Dress with some watercress and serve immediately.