Rinse and soak 1 cup toor dal in plenty of water for an hour
Drain fully and let all water drip by leaving it in a colander for 10 minutes. This is important to ensure that there is no added moisture in the next step.
Add to a blender ( preferably a small mixie jar), add the chillies, hing and one tsp of oil and pulse to make a crumble. Do this step in small batches to ensure you do not make a paste. And, no do not add any water. The residual moisture from the soaked lentils are enough.
Add turmeric, salt and mix well.
At this stage, you can either steam it or directly saute it. Steaming - In this method, the lentils get fully cooked and are fluffier. They are also 'healthier' because it does not use any additional oil. The lentils are also more versatile to use and works for steamed, stuffed or sauteed vegetables. This is the best method if you choose to freeze parupu usili. To steam, add water to a pot and place steamer plates ( or idli plates as I use), add lumps of the crumble mixture and steam for 5-6 minutes. Sauteeing directly - In this method, you will save time. We eliminate the steaming step. To saute, add 2 tsp of oil to a pan, temper mustard and curry leaves, add the ground mixture and stir continuously until it slightly browns. This step will also take 5-6 minutes only.
Once the cooked usuli is ready, let it cool a bit. At this stage, you can also pulse it again to ensure it is a smooth mixture.
To a pan, add ½ tsp oil and temper with mustard and curry leaves. Add the steamed lentils and stir for a minute. This is only required if you steam the lentils.
Once this is done, you can cool it completely and use in your recipe. At this stage, it can also be frozen in individual portions for up to two months.