Heat oven to 180C or 160C fan.
To make the topping mix the sugars and butter. Then spread it onto the cake tin. Set aside.
To prepare the batter, in a large bowl, mix the softened butter with the sugar with an electric mixer, then add the vanilla, eggs, self-raising flour and baking powder and 2 tbsp piloncillo syrup. Beat until it is soft.
Arrange the sweet potato round wedges on the cake tin (see pic below). Then pour the cake mixture, make sure that it goes in all the spaces. Place in the oven and bake for 30 minutes or until cooked through. Leave to cool down for 5 mins, then turn out onto a plate. Serve warm with sweet mascarpone and cream mixture or vanilla ice cream.