Remove meat to a large platter to catch any juices. Cook sliced onions in pan drippings over medium-high heat until well-browned and caramelized, about 10 minutes. Add a tablespoon of oil, if needed. Remove onions from pan and reserve.

Place brisket and any accumulated juices in pan and layer onions on top and all around.

Preheat oven to 300°.

Stir together water (or water and wine) and tomato sauce. Pour over brisket. Bring liquid to a boil over medium-high heat. When liquid boils, cover pot with lid and place pot in oven. Cook for 3 to 4 hours until brisket is tender. Check occasionally and add more water if the liquid evaporates.

When brisket is tender, remove the pan from the oven. Transfer brisket to a large platter, cover with foil and keep warm, reserving cooking liquid from roast.

Cut potatoes into quarters. Place carrots and potatoes in pot roast liquid and simmer over low heat, covered, about 15 minutes until potatoes and carrots can be pierced easily with a fork.

Adjust seasoning with salt and pepper. If a thicker gravy is desired, sprinkle instant dissolving flour into gravy, stirring constantly. Cook over low heat just until thickened. Remove from heat and keep warm.

Slice brisket against the grain 1/4- to 1/2-inch thick. Serve brisket with potatoes, carrots and plenty of gravy.

Variation: For a sweet and sour style pot roast, omit red wine and replace with 2 tablespoons packed brown sugar and 1/4 cup apple cider vinegar to cooking liquid.