This delicately spiced and unbelievably tender brisket is perfect for Shabbat night or any festive meal. Please take care to keep the meat and sauce separately in the refrigerator to keep the meat from drying out.
Remove the beef, reserving the marinade. Pat dry with paper towel, but leave the spices on the meat.Put 3 T. of oil in a large, heavy pot over medium-high heat. Brown the brisket on both sides for a total of about 6 minutes. Remove the beef, and add the onion to the pan and lightly brown. Stir in the vinegar. Remove the onions and add the remaining tablespoon of oil. Add the musthrooms and lightly brown. Remove the mushrooms. Add the marinade to the pot; add the stock, and paprika. Bring to a simmer. Return the brisket to the pot, baste, and cover. Bake in the preheated oven for about 2 hours. Add the onions and mushrooms, and bake, covered, until beef is tender. Remove the brisket from the pan. If you are eating it immediately, slice the brisket thinly and serve with the reserved sauce. If you are eating this at a later time, wrap the brisket tightly in foil and refrigerate. Put the sauce and vegetables into a smaller pan, and refrigerate. To warm and serve, slice the brisket thinly, place in a 9x13 pan, and cover tightly. Warm in an oven, until just heated through. Do not over-cook.
Serve with rice or barley or noodles to take advantage of the delicious sauce. Refrigerate the meat separately from the sauce to keep it from drying out.