Add the onion, carrots and garlic to the pot. Cook until softened a bit. Add the beef and chicken stock.. Place the roast back in the pot. Add the Worcestershire, Thyme, bay leaf and beef bouillon. Bring to a boil. reduce heat to low and cover. Cook 3 to 4 hours until the meat falls apart. Remove the meat from the pot and cut into pieces. With a immersion blender blend the cooking liquid. Strain the liquid through a fine mesh strainer into a fat separator. Keep the solids and add them back to the pot. Add the defatted stock back to the pot with the debris. Add the meat back to the pot. Bring to a boil and reduce to a simmer.