Take water in a sauce pan and heat it till it boils. Once it reaches a good boil, take it off the heat and add in salt and oil. Add in rice flour and make it into a dough. Cover it and let it rest till it gets warm.
While the dough is cooling, take sesame seeds in a kadai and roast it till it pops.
Now add in jaggery and coconut and mix well on medium heat till it gets thick. Add in cardamom powder and mix well. Once it gets thick, remove it to a bowl and let it cool.
Now take the dough in a bowl and Knead it well. Divide into equal portions.
Take a ball and spread it thinly, place a spoonful of filling in the center and cover it carefully and pinch the top to form a modak shape.
Place this in a steamer plate and steam for 8 to 10 mins. Remove it carefully and let it cool.