Cook finely chopped tomatoes with a little water and salt in a pan. Should take about 5 minutes to get squishy. Mash with the back of a ladle.
Soak horsegram or kollu in water overnight. Now pressure cook with 2 cups of water till the horsegram is cooked. Strain the water to use in rasam.
In a blender, blend together garlic, peppercorns and one ladle full of cooked kollu or horsegram. If you wish, you could blend the squished tomatoes here as well.
Now put this back on the fire with 2 cups of strained kollu water. Add salt to taste along with cumin powder and cook out for 4-5 minutes.
Add more water if the rasam feels thick.
Now heat oil and add mustard seeds. Allow to sputter. Add the remaining ingredients and let them cook for a few seconds.
Pour into the hot rasam. Garnish with coriander leaves and serve hot with rice.
Notes
I like to sprout my kollu or horsegram. It ups the nutrition of the grain.
To make ulava charu, don't use tomatoes. Just add 1 tbsp. tamarind paste to the boiled horse gram blended with horse gram water along with other spices and make the same recipe.
I also make a simple stir fry of the boiled horsegram to go with the food.
You may use one tbsp. of tamarind extract if you like your rasam to be more tart. I prefer the sourness from tomatoes.
This is a tasty and very comforting rasam recipe that is also very good for you.