olive oil
In a large pan, heat olive oil on medium heat, then add cumin seeds and wait until they start sputtering.
Add onion puree and cook until it's golden brown (about 15 minutes).
Add the garlic and ginger, and saute for 2-3 minutes.
Add the pureed tomatoes, turmeric, coriander, cumin, garam masala, and salt, and cook on high heat while stirring continuously for 2 minutes.
Reduce the flame to simmer and cook for another 20-25 minutes with the lid on, then serve or store.