Rinse oxtails and pat dry; trim off and discard excess fat. Sprinkle lightly all over with salt and pepper, and place in a 12- by 17-inch roasting pan. Bake, uncovered, in a 450° regular or convection oven, turning once with tongs, until oxtails are well browned all over, 30 to 40 minutes total.
Add wine, broth, 1/4 cup vinegar, rosemary, tarragon, and thyme to pan. Stir gently to mix and scrape browned bits free. Cover pan tightly with foil.
Bake in a 325° regular or convection oven until meat is very tender when pierced, 2 1/4 to 2 3/4 hours.
Mound mashed potatoes equally in the centers of four wide, shallow bowls. With tongs, lift oxtails from braising liquid and arrange equally around mashed potatoes. Scatter caramelized vegetables over meat, cover loosely with foil, and keep warm in a 200° oven.
Skim and discard any fat from braising liquid. Boil, uncovered, over high heat, stirring often, until reduced to 3 cups, 12 to 14 minutes. Meanwhile, in a small bowl, mix cornstarch with 2 tablespoons water until smooth. Stir into braising liquid, and stir until mixture boils and thickens. Taste and, if desired, add 1 to 2 more teaspoons vinegar.
Ladle sauce over meat and caramelized vegetables; garnish with thyme sprigs. Add salt and pepper to taste.
Yukon Gold Mashed Potatoes. Peel 2 pounds Yukon Gold or russet potatoes; cut into 2-inch chunks. Combine potatoes and about 1 quart water in a 3- to 4-quart pan. Cover and bring to a boil over high heat; reduce heat and simmer until potatoes mash very easily, about 20 minutes. Drain potatoes and return to pan.
Meanwhile, warm 3/4 cup milk or half-and-half and 2 tablespoons butter or margarine in a microwave-safe container in a microwave oven at full power (100%) until just steaming, or warm in a 1- to 1 1/2-quart pan over medium heat. Add milk mixture to potatoes and mash with an electric mixer on medium speed or a potato masher until smooth. Season to taste with salt and pepper. Serve, or cover and keep warm in a 200° oven until ready to use. Serve warm or at room temperature.
Caramelized Root Vegetables. Peel 2 carrots (about 3 oz. each) or 12 baby carrots (max. 3/4 in. thick), 1 parsnip (about 6 oz.) or 12 baby parsnips (max. 1 in. thick), 1 turnip (about 8 oz.) or 12 baby turnips (max. 1 in. wide), and 1 lb. pearl onions or 12 cipollini onions (max. 1 1/2 in. wide; or use 10 oz. frozen pearl onions, thawed). Cut carrots and parsnip crosswise into 1/2-inch-thick slices and turnip into 3/4-inch dice; if using baby vegetables, leave whole. In a 9- by 13-inch pan, mix vegetables with 1 1/2 tablespoons olive oil and 1 tablespoon chopped fresh thyme leaves. Sprinkle lightly with pepper. Bake in a 450° regular or convection oven, turning vegetables occasionally with a wide spatula, until well browned and tender when pierced, about 30 minutes. Add salt to taste. Serve warm or at room temperature.
Per serving: 266 cal., 47% (126 cal.) from fat; 31 g protein; 14 g fat; 1 g carbo (1 g fiber); saturated fat, sodium, and cholesterol data not available.