Please refer Rasam(saaru) . The only difference is that you do not add dal. The procedure is simple. After the tamarind water is boiled thoroughly with tomatoes and rasam powder add water that is left over from the cooked dal. The other optional thing is we add 2 tbsp of jaggery. Kattu saaru has a mixture of sweetness(jaggery), spicyness(rasam powder), and sourness(from tamarind).