Pat meat dry with a paper towel and rub with 2 tablespoons flour and salt. Heat oil in a large Dutch oven over medium-high heat. Brown meat on all sides. Add the sliced onions, cover, and reduce heat to low. Cook for about one hour, adding a little water if necessary. Turn meat twice during the roasting process.
Place beets in a saucepan with water to cover. Bring to a boil over medium heat and cook until beets are tender. Drain, reserving liquid. Chop beets into cubes and add to the roasting pan. Add prunes and beet water, cover, and simmer for 5 minutes.
Remove roast to a platter. Mix 1 tablespoon of flour with sour cream. Pour into roasting pan and mix well, scraping the sides and bottom. Simmer until sauce thickens. Season with paprika and taste. Adjust seasoning if necessary.