How to Make It
Fill a large stockpot with 2 inches of water, add 1 teaspoon of the salt and bring to a boil over high heat. Put the lobsters in the boiling water, head first, and cook until they start to turn red, about 4 minutes. With tongs, transfer the lobsters to a bowl to cool; reserve the cooking water.
Remove the meat from the lobster knuckles and claws. Twist the tails off the bodies. Split the tails lengthwise and remove the tail meat. Pull out and discard the black intestinal vein, then cut the tail into large pieces. Cover and refrigerate the lobster meat.
Return the lobster shells to the liquid in the stockpot and simmer over moderate heat for 20 minutes. Strain the broth into a bowl and let stand for 10 minutes. Pour off and reserve 6 cups of the broth, leaving behind any grit at the bottom.
In a large saucepan, melt 2 tablespoons of the butter. Add the pancetta and cook over moderately low heat until lightly browned, about 5 minutes. Add the fennel and cook, stirring, until wilted, about 3 minutes; transfer the pancetta and fennel to a plate. Add the leeks to the pan and cook until translucent, about 5 minutes. Add the wine and boil until reduced by one-third, about 4 minutes. Add the reserved lobster broth, cream, jalapeño and the remaining 1/2 teaspoon of salt. Bring to a boil over moderately high heat. Add the corn and simmer until tender, about 10 minutes.
Remove from the heat and let cool for 5 minutes. Working in batches, coarsely puree the soup in a blender. Return the soup to the pan and add the pancetta and fennel. Season with salt and pepper and keep warm.
In a grill pan or skillet, melt the remaining 3 teaspoons of butter over moderately high heat. Add the lobster meat and cook until lightly seared and heated through. Season with salt and pepper.
Ladle the soup into shallow bowls, garnish with the lobster and chopped chervil and serve.