Preheat the oven to 350°F in time for the oven poaching. Pat the fish dry in paper towels; go over it carefully with your fingers to remove any remaining bones. Score the skin sides . Season lightly with salt and pepper.

Sprinkle half the shallots in the bottom of the buttered baking dish and lay in the fish, skin side down and with the pieces slightly overlapping. If the fillets are very large, fold them in half. Spread 2-1/2 cups of lightly seasoned fresh tomato pulp (tomatoes peeled, seeded, juiced, diced) over the fillets. Sprinkle the remaining shallots over the top of the fish. Pour in enough liquid to come two thirds of the way up the fillets, and lay over them the wax paper, buttered side down.

Ahead-of-time note: Refrigerate if you are not proceeding almost immediately.

Set the dish over moderate heat just until the liquid starts to bubble, then place in the lower third level of the preheated oven, where it should start to bubble slowly in a minute or so. The fish is done when its translucent flesh has turned to opaque, or milky white about 5 to 7 minutes - folded fillets will take a few minutes more.

Remove from the oven. Set the cover over the wax paper and drain the cooking juices into the saucepan. Boil down the liquid to 2 tablespoons, and whisk in from 2 to 8 tablespoons of butter, as for the preceding butter sauce. Rearrange the fish and tomatoes nicely in the dish or on hot plates, spoon the sauce over, and serve.