The tarka this time is of cumin and mustard seeds, but they provide only the background taste. It is the tomato-cream sauce, flavored with the aromatic garam masala, that provides for the main flavors in this dish.
Sesame seeds are packed with protein; toasting brings out their nutty flavor. Tahini is a paste made from ground sesame seeds with a consistency similar to peanut butter; look for it in the Asian section of your grocery store.