Put refined flour, rice flour, baking powder and salt in a bowl and mix. Add buttermilk and whisk well into a smooth batter of dropping consistency. Rest the batter for some time.
Heat one and a half teaspoons oil in a non-stick pan, add mustard seeds, curry leaves and onion and sauté till the onion turns translucent.
Add turmeric powder, mix well and saute for a minute.
Add potatoes and mix. Add salt, mix well and cook for a minute. Switch off heat.
Heat one teaspoon oil in another non-stick pan, pour a ladleful of batter and spread into a pancake. Cook till the underside turns golden. Flip and cook till the other side is also equally done. Similarly make more pancakes.
Place each pancake on a worktop and put a generous portion of potato mixture on one side and roll.
Arrange them on a serving plate and serve immediately.