To make brisket in the Crock-Pot, sear the brisket, place it in the Crock-Pot, and add 2 sliced onions cooked in olive oil. Add 2 cups of beef broth, 2 tablespoons of Worcestershire sauce and 1 tablespoon of soy sauce. Cover the ingredients, and cook for eight hours on low.
Because brisket is one of the tougher cuts of beef, cooking it slowly in a Crock-Pot makes it tender and flavorful. Place 2 thinly sliced yellow onions and 4 ounces of freshly sliced mushrooms into the slow cooker, adding enough water to cover the bottom of the cooker. Place the brisket fat-side up onto the onions and mushrooms. Sprinkle it with garlic flakes, and spread over it a mixture of 2 tablespoons of tomato paste, salt and pepper to taste and 1 tablespoon each of Worcestershire sauce, red wine vinegar, balsamic vinegar and brown sugar. Cover the ingredients, and cook them on low heat for eight to 10 hours.
Remove the brisket to a serving plate, add cooked onions and mushrooms, and cover it tightly with foil. To make the gravy, turn the heat setting to High, remove half the liquid, mix it with 1/4 cup of flour until well-blended, and return the flour mixture to the juices in the Crock-Pot, cooking and stirring until thick. Serve the gravy on the side with the brisket.