Firstly, in a large kadai heat 2 tsp oil and splutter mustard seeds and few curry leaves. Add chopped onion, green chilli and ginger paste. Saute slightly until the onions shrink. Add the chopped carrot pieces and saute until cooked. Now add turmeric and required salt. Saute for a minute until the raw flavor of turmeric goes away. Add grated potato and mix well. Mix and mash until everything is well combined. Aloo masala stuffing is ready. Keep aside.
Mix the idli batter gently by adding required salt.
Fill half the greased idli mould with idli batter.
Make some small balls out of the also masala.
Place a small ball sized aloo masala over the batter. Make sure to adjust the size of aloo masala based on the size of idli stand.
Cover the aloo masala with idli batter.
Cover and steam for 15 minutes or until the idli is cooked completely.
Finally, enjoy stuffed idli with a coconut chutney or as it is.