How to make Mexican candied yams?

There are these big chunks of yam or sweet potato that are concealed in a heavy sugary, yammy candy shell at a burrito place here in LA. I have never seen them anywhere else but I am obssessed with it! Sadly, thier burrito's are not as good as so many other places. Do you know how to make them? They can be picked up and eaten. They are not sticky or gooey on the outside. Thanks so much!