The sourness in this rasam or saaru as it is called in Kannada comes from tamarind paste .I have used kokum in this recipe as kokum is a good replacement for tamarind except that it is less sour than tamarind.
Ingredients : 6-7 kokum pieces, 2-3 cups water, 1/2 tsp black pepper powder, 1 tbsp tsp ghee, 1-2 byadgi mirchi broken into pieces, 2-3 sprigs of curry leaves, 1/2 tsp mustard, 1/2 tsp jeera, 1/4 tsp haldi, 1/4 tsp hing, 1 tbsp gur or jaggery, salt to taste.
Method : Take a pan .Heat it. Add ghee. After it melts, add mustard.After they pop up, add jeera. followed by byadgi mirchi & curry leaves.Add pepper powder.Add hing & haldi & mix all nicely. Add 2-3 cups water.Add kokum pieces.Add jaggery ( grate jaggery if jaggery is very hard or add by breaking jaggery into smaller pieces ).Let all come to a boil.Let it boil for 5 minutes. Add salt. Mix nicely.Let it come to one more boil so that salt has mixed nicely. Put off gas. Serve goda saaru with monng dal khicdi or plain rice with ghee. Goda saaru can be drunk just like that to give relief top sore throat.