To make the cake, preheat the oven to 180℃.
Add the sugars, maple syrup, oil and eggs in a large bowl and whisk until smooth.
In another bowl add the flour, baking powder, baking soda, salt, cinnamon, nutmeg, pecans and stir to combine.
Add the dry ingredients into the wet ingredients in 3 parts. Alternating with the mashed sweet potato. Keep whisking until smooth.
Line a 9 inch round cake tin with a little baking spray and baking paper. Pour the batter into the tin.
To make the crumble: Mix all the ingredients in a small bowl until lumpy but combined. Sprinkle over the cake batter.
Bake the cake for 1 hour. Check the cake after 45 mins by poking a knife into the center. If it comes out clean it is baked, if not then bake it some more. The knife should come out clean.
Once the cake is baked remove it from the oven and let it cool completely. Ideally on a wire rack.
To make the icing: whisk all the ingredients together until smooth. If the icing is too thick add a drop of water to thin it out. If it is too thin add a tablespoon of icing sugar to thicken it up.
Drizzle the icing over the cake, slice and serve. Enjoy with tea or coffee.