Parupu urundai kulambu is one of the popular veg gravies of Tamilnadu made by cooking spiced lentil balls in a tamarind based curry.
1) You can steam the balls for 10mins before adding them to the gravy. In that case, reduce the total cooking time of the kuzhambu.
2) Do not do coarse grind as the balls tend to brittle and lose their shape. While cooking the balls make sure the heat reaches its center. Keep the heat medium and cook well. Before switching off, you can break one ball to check the inner part.