Heat oil in a pan and add cumin seeds. Let them splutter.
Add chopped onions and sauté until golden brown.
Add ginger, garlic, and green chilies. Sauté for a minute until aromatic.
Now add cilantro stalks and mint. Saute until they soften.
Stir in the chopped tomatoes and cook until they turn soft and mushy.
Add turmeric powder, coriander powder, cumin powder, red chili powder, black salt, amchur powder, and salt. Mix well.
Add about ¼ cup of cooked white peas to the pan. This will help thicken the curry.
Blend this mixture into a smooth paste using a mixer grinder (add a little water if needed).
Return the paste to the pan and add the cooked potatoes, and white peas along with the water used for cooking them.
Simmer the gravy for 8-10 minutes, mashing some peas to thicken the consistency.
Finish with garam masala, chaat masala, and fresh coriander leaves. Adjust seasoning as needed.