The sauce is a tomato- and onion-based sauce that is simmered until smooth and much of the water has evaporated. There are many variations on the composition and spicing of the sauce, which is sieved so that it is velvety smooth. Spices may include cardamom, cumin, cloves, cinnamon, coriander, pepper, garam masala and fenugreek (Punjabi/Hindi: kasuri methi).