How to Make It
Preheat the oven to 450°. Rub the duck inside and out with salt. Let stand at room temperature for 30 minutes.
Set the duck, breast side down, in a very large enameled cast-iron casserole. Pour the wine on top and add the peppercorns, garlic and bay leaf. Braise the duck uncovered in the oven for 20 minutes, until it starts to brown. Turn the duck breast side up, sprinkle with salt and add the tomatoes and grapes. Braise uncovered for 20 minutes. Reduce the oven temperature to 300°. Cover the casserole and braise the duck for about 45 minutes longer, until an instant-read thermometer inserted in the thickest part of the thigh registers 160°.
Transfer the duck to a rimmed baking sheet. Strain the pan juices into a saucepan; reserve the tomatoes and grapes and discard the remaining solids. Skim off the fat and boil the juices until reduced to 1 cup, 20 minutes. Add the cherry tomatoes and grapes; season with salt and pepper.
Preheat the broiler. Using poultry shears or a large, sharp knife, cut the duck in half. Arrange the duck halves on the baking sheet, skin side up. Broil the duck 6 inches from the heat for about 4 minutes, rotating the pan as necessary, until the skin is crisp. Carve the duck and serve with the pan sauce.