Heat 2 tablespoons of oil in a kadhai. Fry badi (vadi) over low heat till they become deep brown from all sides. Transfer them to a plate and set aside.
In the same kadhai heat remaining mustard oil. Once the oil is hot, add cumin seeds, chopped garlic, and coriander stalks. Fry them for 30 - 40 seconds or till garlic is nicely roasted.
Add flour, and start roasting it over low heat until it turns light golden and a nutty, roasted aroma is released. Add spices, salt, and stir to combine.
Now, slowly add water and from the other hand continuously stir the curry in circular clockwise motion to avoid lump formation.
Add fried badi into the curry.
Bring the badi ki sabji to a boil over high heat, now let it simmer over low heat for the next 20 minutes, stirring at regular intervals. You will notice after sometime the curry is thick, luscious, reduced to half, and a thick layer starts forming on top. That is the signal badi ki sabji is ready.
Add chopped coriander leaves and a tablespoon of ghee (optional).
Serve badi bhaat warm for lunch.