Soak urad dal and rice overnight
In the morning blend the urad dal and rice and make a smooth paste.Rest this batter again for 1-2 hours.
After that add water, salt and black pepper according to taste and make dosa in the pan
Heat butter in a pan
Add mustard seeds,curry leaves, onion and green chilli
Put salt,haldi and mashed potatoes in it
Mix it well and the masala aloo is ready