Lightly grease a 17-cm round cake pan with a little oil, or if making cupcakes, line 7 round tartlet tins with paper muffin cases. Sift flour and baking powder together. Set aside.
Combine beet sugar and soy bean paste in a bowl and mix well. Add yam and beat to combine. Add water and oil and mix well. Add flour mixture and fold in with a spatula. Fold in chestnut