Heat oil in a large pot over medium heat. Add in cumin seeds, bay leaves, green chili and ginger. Let simmer for 30 seconds. Next add in peas, sesame seeds, garam masala, chat masala and black salt. Mix well. Add in potatoes. Using a rubber spatula, mash the potatoes while mixing. Add in lemon juice, cumin, amchur powder, milk, sour cream and cilantro. Mix well to incorporate all ingredients. (Should take about 5-7 minutes in total to make the mixture) Once done, set aside.