In the bottom of a slow cooker, add butter.
Next, place potatoes, carrots, and onions.
Place the sirloin tip round roast on the vegetable bed.
In a microwave-safe bowl, add beef stock, tomato juice, apple juice, corn starch, and Worcestershire sauce. Mix well.
Add Herbs de Provence, garlic powder, parsley, salt, and black pepper and stir.
Place the bowl in the microwave for about 90 seconds.
Once it is done, it will have a thick consistency. Pour this mixture over beef and vegetables.
Seal the slow cooker with lid and cook on low temperature/option for about 8 hours or until the beef roast is completely cooked and falls apart.
Serve hot.