Heat up a pan and pour a few tablespoons of vegetable oil. Add the cumin seeds, when you smell them, add the cinnamon, cardamom and mace. Saute for 20 seconds. Add the onion, a little salt and saute until golden. Add 2 tsps garlic, 1 tsp ginger, saute for a minute, add 2 tbsps butter, the chopped tomatoes, a little salt. Cover and cook until tomatoes are soft and you can mash them easily. Stir occasionally. When the tomatoes are done, leave it aside to cool a little bit before blending. When cool, blend until smooth. Pour the blended mixture into a sieve and strain to make a creamy, smooth sauce. Don’t forget to scrape off all the sauce on the outside.