Cook in the oven the sweet potatoes until soft. Remove from the oven and peel them. Place the meat into a dish, smash to reduce to a no chunk pulp and let it cool.v
Keep the oven at 400°.v
Mix all the flour, baking powder, salt, sugar, cinnamon and chocolate chips if using.
Add to the dry ingredients the orange juice, sweet potatoes, egg and oil and mix well.
Place muffins cups in muffins pan and pour muffins mix up to cup high.
Sprinkle sanding sugar and bake in the oven for 15 to 20 minutes, or until the toothpick comes out clean.
Serve at room temperature.