Take jaggery in a sauce pan add water, mix well with a laddle for the jaggery to dissolve.
Filter to remove impurities.Then pour it back to the pan and heat it up to thicken a bit.
Pressure cook channa dal for 4 whistles and mash it with a laddle or masher.Then add this to jaggery syrup.
Cook till it thickens.The more the water you add to jaggery it will take more time to get thicken, so be careful while adding water.
At one stage the mixture will become thick leaving the sides of the pan.
This is the right stage, add cardamom powder, mix well and switch off. When it is still warm, roll them into small balls. Keep aside.
Add salt to rice flour, Mix it once. Boil water until it bubbles up, switch off then add it to rice flour.
Mix with a laddle, once it starts to come together, Set aside for few mins until it is warm enough to handle with hand. Now bring everything together to form a smooth dough without any cracks.
Now the stuffing and the outer dough is ready. Take your mould, grease it with oil, grease your hands too. Now close the mould and take a dough shape it as a ball and stuff it from the bottom side.
Nicely press it along the sides in the inner part, leaving a center hole for the stuffing. Now carefully insert the stuffing in the center hole, press it. Then seal it with little dough as shown.
Then open carefully to take out the modaks. Grease the mould with oil when it starts sticking. Repeat the process till the entire dough finishes.
If you don't have mould you can shape modaks like this(for detailed steps check below).Then arrange all the modaks it in idli / idiyapam steamer and steam it for 8-10 mins. When the outer layer turns shiny then your modaks are done.