1. Preserved sweet potatoes can be cooked in water or oil. In fact, they are almost the same. Boiling means putting a little water without oil, and cooking in oil means putting a little oil and then putting water. Whether to add gas or not depends on personal preference.

2. Add a little more sugar, then add twice as much water, stew slowly, and stir constantly while stewing. When sugar water is boiled to a certain extent, it will boil and many big bubbles will appear. With the decrease of moisture, the sugar juice will become thicker and thicker, and the viscosity will become higher and higher. Large bubbles become smaller and more uniform, usually caramel color.