1. Cut ¼ inch from the stem end of the tomatoes, scoop out and discard the seeds. Carefully scoop out the inner pulp with a sharp spoon or melon baller, leaving the outer walls of each tomato intact. Roughly chop the pulp and set it aside. Lightly salt the shells and invert them over a colander to drain.

2. Bring 2 quarts of water to a boil and add a large pinch of salt and the shrimp. Cover for 2 minutes, then immediately drain the shrimp. (If the water returns to a boil before the 2 minutes is up, drain the pot immediately.) Rinse shrimp under cold water and peel. If shrimp are not small, chop them into 2 or 3 pieces each. Pick over the crabmeat for bits of shell.

3. Heat 2 tablespoons of the butter and all of the onion in a saute pan over medium heat and saute, tossing until it is translucent, about 4 minutes. Add the garlic and saute until fragrant, about 30 seconds. Add reserved tomato pulp and cook until it begins to break down and its juices begin to thicken, about 4 minutes. Add parsley and basil and the 1 cup coarse crumbs and toss well. Remove pan from heat. Add crab and shrimp and toss until evenly mixed. Season well with salt, pepper, cayenne and nutmeg.

4. Position rack in center of oven. Heat oven to 375 degrees. Butter a 9-inch square casserole. Gently wipe insides of tomatoes with a paper towel and place, open side up, in casserole. Divide the seafood mixture among the tomatoes.

5. Wipe out the pan in which the onion and tomato were cooked. Add remaining 1 tablespoon butter and melt over low heat. Add the fine crumbs and toss until evenly mixed. Sprinkle the fine crumbs over the tops of the tomatoes. Carefully pour boiling water around the tomatoes until the water comes not quite halfway up the sides. Bake until the shells are barely cooked and the filling is heated through, about 20 minutes.

Makes 4 servings.