Make the dough for the Poli:
Mix all the ingredients, then add enough water to knead into a fairly soft, slightly sticky dough. You want a sticky dough so you can roll out your polis quite thin, the way they should be.
Place in a box with a fitted lid and set aside for at least half an hour.
Make the puran:
Place the drained, cooked chana dal and the jaggery in a food processor and process until you have a fine paste. DON'T add any water.
Heat the oil in a heavy skillet. Add the powdered chana dal and jaggery and cardamom powder and cook, stirring constantly. The mixture will begin to thicken up and you want it to go until it's just beginning to come off the sides and bottom of the skillet, but is still sticky and not powdery.
Set the puran aside. When it is cool enough to be handled, shape into 1-inch balls and set aside.
Make the Puran Poli:
Now take the dough you prepared earlier for the poli and break off a piece, about half the size of the ball of puran.
Roll it out, using as little flour as possible, into a disc about 3 inches in diameter.
Place the ball of puran in the center and pull the edges of the dough over the top and seal the ends together. The puran should be completely ensconced in the dough.
Flatten the ball gently and, again using as little flour as possible, roll it into a disc about 6 inches in diameter.
Heat a griddle and place the poli on it. Cook until golden-brown spots begin to appear at the bottom and the poli begins to puff up. Flip over and cook the other side until done.
You can brush the poli with a little oil, if you like, although that's really not necessary.
In Maharashtra, puran polis are traditionally eaten with Kathachi Amti, a spicy, watery concoction made with the stock left over from boiling the chana dal, or with some ghee or milk. I love dunking it in vanilla soymilk...bliss!