Place the sliced onions in the bottom of a Dutch oven. Season the roast with salt and pepper and place it on top of the onions. Add the vinegar and bay leaf to the pan and cook over high heat for about 10 minutes to get the roast simmering. Reduce the heat to low, cover and allow it to simmer over low heat 3 to 4 hours. When it is done, remove the roast from the pan. Mix the flour into the water and pour it into the drippings from the roast. Simmer the gravy over medium heat, stirring it until it thickens. Carve the roast and serve it with the pan gravy.

Serve with mashed potatoes and your favorite veggie side dish to complete a hearty dinner.