Clean mustard leaves properly and wash them twice with water. Place the leaves in a strainer so that all water is removed from the leaves. Cut the leaves into thick pieces and put them in the cooker, also pour 1 small bowl of water and boil. After 1 whistle goes off, turn off the gas and let all of the pressure escape from the cooker.
Make a fine paste of tomatoes, green chillies and ginger.
Pour oil in a frying pan(kadhai) and heat, put Heeng and Jeera in hot oil. After the two are roasted add turmeric powder and gram flour then fry the two. Now put the tomato paste followed by red chilly powder and fry the spices till oil separates from them(if you want you can also put onion and garlic then fry them along with the spices).
Take out the mustard leaves from the cooker, cool them off and grind in a mixer(do not make it excessively fine). Put 1 glass of water and salt in the spices, mix properly by stirring with a spoon. After curry comes to boil cook it for 5-6 minutes on a low flame. Your Sarson ki Bhaji is ready.
Take out Bhaji in a bowl, put butter or Ghee on top. Serve hot Sarson ka Saag with Makke ki Roti, naan, paratha or chapati.