You can use this during the course of the week, but it also freezes well in individual portions for Indian dinners to come. The trick is to keep the sauce relatively light on spices, providing much opportunity for tweaking to recipes later: Add a touch of whole spices here, and a touch of tamarind there, and you’ll never know the same sauce provided a starting point! —Mallika
In a large pot, bring the oil to heat on medium-high. When it starts sizzling around a wooden spoon, add the sugar. As it caramelizes, the onions along with the salt. (The sugar gives the curry a lovely deep red hue, without the need for food coloring and is traditionally used in Bengal, where I’m originally from in India. The salt will help the onions cook to golden beautifully by drawing out the water in the onions.) Cook the onions for 10 minutes.
While the onions cook, peel and mince the garlic and ginger.
Add the ginger and garlic to the onions and cook for another 10 minutes. By this point the whole mixture, i.e. your masala, should be turning golden.
Chop the tomatoes into small cubes and add them in, along with the turmeric and chile powders. Stir this mixture well for another 15 minutes ,until the tomatoes disintegrate.
Finally, lower the heat to a high simmer, cover, and cook for 5 minutes, until you see oil oozing out of little pores on the surface of the masala.
Test for salt, adding it to your taste.
Cool and store in 1/2-cup portions. This should last 3 to 4 days in the refrigerator and up to 2 months in the freezer.