If desired, line a 6 quart or larger slow cooker with a liner.
Whisk beef stock, Worcestershire sauce, apple cider vinegar and spicy brown mustard together. Pour into the slow cooker and arrange the onions in a layer on top.
1 cup beef stock, 1 tablespoon Worcestershire sauce, 1 tablespoon apple cider vinegar, 1 teaspoon spicy brown mustard, 1 large onion
Then combine the garlic powder, onion powder, paprika, dried thyme, dried rosemary, salt and pepper together and spread over the beef roast.
1 tablespoon garlic powder, 1 tablespoon onion powder, 1 tablespoon paprika, 1 teaspoon dried thyme, 1 teaspoon dried rosemary, ½ teaspoon salt, ½ teaspoon pepper
Place the roast into the slow cooker and add the cranberry sauce and fresh cranberries.
2.5 lb beef roast, 14 oz cranberry sauce, ½ cup fresh cranberries
Cook on low for 8-10 hours, then shred the beef.