Boil potatoes until just cooked.
In a small bowl, add 1/3 cup boiling water to the tamarind.
Let sit for 10 minutes. Drain tamarind squeezing out all of the liquid and discard the paste.
Reserve the tamarind water.
Heat oil. Add cumin seed. When they become a little golden and fragrant, add garlic, dried chiles and curry leaves.
Stir fry for 1/2 a minute.
Add onion and chile. Fry until the onion turns golden.
Add turmeric, coriander, cumin and red chile powder. Stir to combine.
Add tomatoes and cook for another 5 minutes.
Add boiled potatoes, jaggery, salt, tamarind extract and 3/4 cup water.
Cover and cook on a low simmer for 10 minutes.