Prepare the sweet potato puree: (using oven or steamer)
To use the oven: preheat the oven to 400 F(200 F) for conventional oven. If you use a convection oven, please lower temperatureby 20 F (15 C)
You will need about 3/4 lb (about 338 grams) of sweet potatoes. Pierce the sweet potatoes all over with a fork and place on a baking sheet lined with aluminum foil (for easy clean up). Roast the sweet potatoes for about 45-50 minutes or until they are fork tender, meaning, you can easily pierce into the flesh and easily mash it too.
Cut the potato into half and remove the skin, scrape the flesh into a food processor and add about 2 teaspoons of water and process into a smooth puree
To use the steamer: bring the water in the steamer to a boil. You can peel the skin of the sweet potatoes, cut into smaller chunks and place on a steamer rack or a heat-proof dish. Steam for 20-30 minutes (depending on the size of the sweet potatoes) or until they are fork tender and can be easily mashed
Transfer to a food processor or use a hand blender and process into a smooth puree. You don't need to add water to puree it, because steaming is a moist heat and the sweet potatoes remain moist enough
Prepare the cake batter:
Lightly grease an 9 x 5 inch loaf pan and line with a parchment paper on the long side, overhanging on the side. You can also use an 8x8 inch square pan and then line with a parchment paper sling
Combine flour, baking powder, and baking soda, and all the spices. Set aside
Combine mashed potato puree, sugar, oil, and orange juice in a large mixing bowl. Whisk vigorously until mixture is well combined.
Add the egg and vanilla extract and continue to whisk until mixture thickens. The egg helps to emulsify the mixture
Add 1/2 of the dry mixture into the wet and switch to a flexible spatula to fold the mixture and continue with the other 1/2.
When the dry and the wet is almost combined, add the chocolate chips and continue to fold until you don't see any dry pockets of dry ingredients. Take care not to overmix though. This is a very thick batter
Scrape the batter into the prepared pan and use a flexible spatula to help you spread it evenly across the pan. Sprinkle with some turbinado sugar
Baking:
Bake in the middle rack for about 45-50 minutes for 9 x 5 inch loaf pan, and about 25-30 minutes for 8 x 8 inch square pan, or until a skewer inserted into the center of the cake comes out clean with just a bit of sticky crumbs is fine, but it shouldn't be wet. The top should be set and not jiggly anymore
Cooling:
Place the baking pan on top of a cooling rack. Let the cake cool in the pan for 30 minutes. Do not remove it from the pan yet as it is still very warm and tender.
Grab the parchment paper sling and carefully set the cake on top of a cooling rack to let it cool completely. Do not attempt to slice when it is still warm as it may fall apart
To serve:
This cake has the best texture and taste the next day. It is very moist and the flavor has deepened significantly. The turbinado sugar adds a nice little crunch on top. Use a serrated knife to cut the loaf cake for the best result