For idli batter: rinse urad and chawal thoroughly with water. Soak it overnight with enough water. Afterwards drain excess water and grind to smooth paste. Keep aside till fermented.

Now for sambhar. :firstly wash toor dal and cubed lauki throughly. In a pressure cooker add dal, lauki, salt 1 tsp and 1 tsp haldi powder.close the lid and Pressure cook upto 5 whistles. Remove from gas stove.Remove the lid and stir it for 1-2 min. Keep aside for tadka.

Take a wok add oil and heat it. When oil is sufficiently heated add mustard seed and heeng. When it starts to crackle add red chilli and onions and saute till onions changes it's colour.

Now add chopped tomatoes and saute till mushy. Now add all the left spices and curry leaves except sambhar masala. Cover the wok and Cook till tender on low flame. When oil starts to separate add sambhar masala and again cook for few minutes till all the flavors are well absorbed.

Now take the previously cooked toor dal with lauki and add tamarind extract and prepared tadka. Add water and adjust the consistency of the sambhar. Boil sambhar for few minutes more on medium flame till all the flavours are well absorbed.

Now for idli:mix salt and water to the idli batter and beat the mixture. So that idli becomes fluffy. Pour the batter to the idli mould. And steam it in a steamer or any big vessel for 5-8 min. Check with the tooth pick.if tooth pick comes out without any batter idli is done.if not continue steaming for few minutes more. Remove from the steamer and Demould it.