Directions

1. Preheat oven to 350 degrees F. Place sheet of heavy-duty aluminum foil in a shallow roasting pan with foil extending 6 inches beyond pan on either side. Spray with no-stick cooking spray. Place the brisket fat-side down in middle of the foil.
2. Combine dry onion soup mix with jelly and cocktail sauce in a medium bowl. Pour half of mixture over the brisket; turn brisket fat-side up covering with remaining onion mixture. Bring both sides of foil to the middle and fold foil down on itself several times. Repeat with the two remaining sides. Bake for 3 hours or until fork-tender. Remove from oven. (Brisket can be cooled and held in the refrigerator overnight at this stage.)
3. In a 10 inch skillet over medium heat, melt 2 tablespoons of butter; saute onions and mushrooms for 5-8 minutes or until light golden brown.
4. Remove brisket from pan; pour off juices skimming the fat off the top. Remove layer of fat from brisket. Slice meat across the grain into 1/4 inch thick slices. Return meat to roaster. Top the meat with the mushroom mixture, meat juices, and tarragon. Cover with foil. Return to oven to heat through before serving.