Wash and soak the chana dal for 6-8 hours. Grind to a smooth paste along with green chillies, ginger paste, salt and sugar, using very little water.
Heat oil in a non-stick pan and add kala jeera and a pinch of asafoetida. Tip in the ground dal mixture and stir quickly on low flame till the dal paste starts to leave the sides of the pan. It should be slightly dry and not runny.
Remove onto a greased plate. Evenly pat down the mixture to about 1 inch depth with greased hands.
Allow the mixture to cool and set well. Cut into diamonds or squares. Heat oil for deep frying. Fry the chana dal cakes on medium flame till they turn a golden brown on both sides. Remove the lentil cakes onto a paper napkin.
Peel and cut the potato into 8 pieces, chop the tomatoes and grate the ginger.
Heat about 2 tbsp oil in a kadai and fry the potatoes till they get a slight colour on them. Remove and keep aside. Add bay leaf, cumin seeds and hing to the pan. Sauté. Add grated ginger and chopped tomatoes. Cook till tomatoes turn soft.
Add ¼ tsp chilli powder, ¼ tsp turmeric, ½ tsp coriander powder and ½ tsp cumin powder. Mix well and cook till oil separates.
Add the potatoes, ½ tsp sugar and salt and ¼ tsp of garam masala. Combine well.
Add 1 ½-2 cups of water and boil till potatoes become soft. Then add the fried lentil cakes and simmer for a minute.
When the gravy thickens and the fried chana dal pieces start to soak in it, add ½ tsp of ghee and remove.
Serve Dhokar Dalna hot with soft, fluffy luchis or white rice.