1. Add mustard seeds, garlic and ginger in a blending jar. add little water and blend it into smooth paste. take it out from the blending jar and keep it aside.
2. Heat little oil in a pan, add chopped potato and fry it for 4-5 minutes on medium flame.
3. Add drumstick and fry it with potato for 2-3 minutes on medium flame.
4. Take out the fried potato and drumstick in a plate and keep it aside.
5. Add oil in the same pan and let it heat properly. add cumin seeds and fry it for few seconds, reduce the flame to low.
6. Put blended masala paste, turmeric powder, red chilli powder, cumin powder and coriander powder. mix it and fry the masala for 2 minutes on medium flame, keep stirring.
7. Add chopped tomato, cover the pan and cook it on low-medium flame for 4-5 minutes, keep stirring in between.
8. Put one glass of water, cover the pan and let the drumstick curry boil on high flame.
9. Add fried vegetables and salt to taste, cover the pan and cook it for 7-8 minutes on low flame.
10. Check the potato with fork / knife (cook it for another 2-3 minutes if the potatoes are not cooked properly)
11. Turn off the flame, drumstick curry is ready to serve with plain steam rice or jeera.