To get mashed sweet potatoes, boil / steam or pressure cook 3 medium sized sweet potatoes until they are cooked. Once cool, discard peel and place flesh in a bowl and mash with a fork or run in a food processor to get a dry mash.
Preheat the oven at 180xb0C. Line a loaf tin with baking paper.
In a large bowl, place the oil and yogurt. Whisk well to combine. Add the mashed sweet potato, lukewarm water, powdered jaggery (or brown sugar), regular sugar and whisk well until combined.
Sieve the flours, spice powders, baking powder and baking soda into a large bowl.
Add the dry ingredients in 2-3 batches into the wet ingredients in the bowl, and fold to combine well, and get a smooth batter.
Scrape out the batter into the prepared loaf tin. Smoothen out the top.
Bake in a preheated oven at 180xb0C for 40 minutes or until a tester comes out clean.
Allow the cake to rest in the pan for 5 minutes after which you can turn it over a wire rack to cool for 15 minutes before slicing.
To prepare glaze, combine icing sugar, cinnamon powder and milk to get a smooth pourable glaze. Using a spoon drizzle this glaze over the loaf.