If you are using fresh tomato, take a separate pan/skillet, and add some olive oil /ghee, chopped tomato (saving 1 for garnish), water, 1 table spoon of oregano and/or thyme (optional) and 1 stock cube. Cook until tomato is well cooked trough, let it cool for a bit and put in the food processor to make a tomato sauce. If you are using canned chopped tomato (400g can), just blend in food processor with 1 table spoon of oregano/thyme. If you don't have either, you can use tomato paste.