Boil the potatoes with salt till they are done. Make sure not to overcook them. They should retain the shape.
Heat oil in a pan and crackle jeera. Add grated/crushed ginger and garlic. Cook for 2-3 mins. Add chopped onion and cook till they become golden brown in colour. Add the masala powders and cook till the raw smell goes, around 2 - 4 mins. Add chopped tomatoes along with salt and sugar, mix well. Add 1/4 cup water and cook. When tomato becomes soft, add cooked potatoes. Add 1/4 cup hot water and combine well. Make sure the potato pieces are coated well with the masala. Garnish with chopped coriander leaves. Serve hot with rice/roti.
Notes
If you are making it for roti, you can add more water in the end. You can also add a dash of lemon also in the end.