Wash and soak the matar in about 3 cups of water overnight. After soaking they will double about 2 and 1/2 times in size. Dry roast the cumin seeds and coriander until they are brown and give a good aroma. Note to roast them separately.
Let it cool and then grind them to a powder consistency. In a pressure cooker, add matar with 2 and 1/2 cups of water, salt, ginger and green chili, then cook it on a medium-high heat. As pressure cooker starts steaming turn the heat down to medium.
Cook it for about 8-9 minutes, then turn off the heat and wait until the steam releases before opening the pressure cooker. The matar should be soft and tender. Next, add in all the spices, this is the time to adjust the salt and pepper to your taste.
Mix it well together. Add a little water if it looks too dry, it should have a thick gravy.
To make the aloo patties, boil the potatoes, then peel and mash them. Add the green chillies, ginger, red chilli powder, salt, coriander leaves and mix it well. Add salt to mashed potatoes and mix again. Divide it into eight equal portions.
Heat a tawa. Take a portion of the mashed potatoes in your palm, spread it slightly in the edges and shape into a tikki. Shallow fry the tikkis on a medium heat with a little oil till both sides are evenly golden brown. If the potato covering breaks add a little cornflour and mix.
To plate, placethe tikki on a plate. Pour some chilled yogurt, green chutney, sweet tamarind chutney over it. Sprinkle the roasted cumin powder, chaat masala, red chilli powder and chopped onion on top and serve.