In a large bowl, whisk together the white rice flour, brown rice flour, besan, sweet white rice flour, potato starch, xanthan gum, baking powder, and baking soda. Gradually stir in the rest of the ingredients, as they are ordered, and whisk until very smooth. Drop a little less than ⅓ cup batter into the prepared baking trays and bake for about 27 minutes, or until knife inserted into the centre comes out clean. Remove cupcakes from the pan and let them cool completely on a rack before frosting. Store covered in airtight container for up to 2 days.