Burnt jubbly is the result of accidentally burning a raw jubbly while attempting to make a cooked jubbly. Cooking a cooked jubbly requires 41 Cooking, and burning it will become less common with a higher Cooking level. It must be cooked on an ogre spit roast.
The burnt jubbly has no use whatsoever. Like most other burnt food, it is tradeable to other players but not on the Grand Exchange.
After a certain Cooking level, it is no longer possible to burn a jubbly without temporarily reducing one's Cooking level.