How to Make It
In a food processor, combine the softened butter with the parsley, 1/2 tablespoon of the tarragon and the chives. Season with salt. Transfer the herb butter to a large piece of plastic wrap, form into a cylinder and refrigerate.
In a medium saucepan of boiling water, cook the lima beans with the onion, thyme sprig and a pinch of salt over moderate heat until the lima beans are tender, about 10 minutes. Drain and discard the onion and thyme.
In a food processor, puree the beefsteak tomatoes. Strain the puree into a medium bowl; you should have about 1 1/2 cups of tomato puree.
In a large skillet, melt 2 tablespoons of the butter. Add the shallot and cook over moderate heat until softened, 2 minutes. Add the corn, ham and Old Bay seasoning and cook, stirring, for 2 minutes. Add the Champagne and simmer over moderately high heat until reduced by half, 3 minutes. Add the diced tomato, lima beans and tomato puree. Simmer over moderate heat until flavorful and the liquid has thickened slightly, 4 minutes. Remove from the heat.
In a large skillet, heat the oil until nearly smoking. Season the cod with salt and pepper and cook, skin side down, over high heat until the skin is browned and crisp, about 4 minutes. Turn the fish, reduce the heat to moderately low and cook until just opaque throughout, about 3 minutes longer.
Stir the crabmeat and the remaining 1 tablespoon of tarragon into the stew; simmer for 1 minute to heat through. Off the heat, swirl in the remaining 2 tablespoons of butter; season with salt and pepper. Spoon the stew into bowls and set a cod fillet in each. Top each fillet with the herb butter and serve.