Step 1

Combine seasoning, tomato paste, sugar and vinegar in a bowl.

Step 2

Arrange onion in a lightly greased slow cooker. Coat the beef in the Mexican paste and place on top of the onions. Pour stock around beef (don’t pour stock over beef). Cover and cook on HIGH for 8 hours. Transfer beef to a roasting tray. Using 2 forks, roughly shred.

Step 3

Transfer the liquid from the slow cooker to a large saucepan. Simmer over medium-high heat for 5 to 10 minutes or until the sauce thickens and is syrupy. Strain onions and scatter over beef. Pour over half the sauce and reserve remaining sauce to serve with tacos (see notes).