Rinse and soak lentils in hot water while you prepare other ingredients.
Saute Aromatics and Pressure Cook
Turn on Sauté on High. Add oil and heat for 30 seconds. Add heeng followed by mustard seeds.
When mustard seeds begin to splutter, add curry leaves, onion, ginger, and garlic. Sauté for 3 minutes, until the onions soften a little.
Add chopped tomatoes along with salt, turmeric, coriander and sambar powder.. Sauté for 2 minutes till the tomatoes break down. Add ¼-⅓ cup water and deglaze the pot. Scrape off any brown bits stuck to the bottom.
Add rinsed and drained lentils along with the chopped vegetables. Add water and stir. Turn off Sauté.
Lock lid in place in sealing position. Set pressure cook or Manual for 10 minutes at High Pressure on sealing mode. For a mushier texture, adjust time to 12 minutes. When the cooking time is up, let the pressure release naturally for 5 minutes, followed by a quick release as per your cooker instructions. Unlock and remove the lid.
Add Finishing Flavors
Stir in tamarind concentrate, sugar (if adding) and check for seasoning. Using the back of a ladle or potato masher, mash the lentils to get a creamy texture. Let the curry rest for 2 to 3 minutes. Garnish with cilantro and serve with Steamed Basmati Rice.
Alternative Method: Pot-In-Pot Vegetables
Add the ingredients for sambar, except the vegetables, in the Instant Pot steel insert as per directions above.
Insert the trivet into the Instant Pot, then place a steamer basket on top and add veggies.
Close the lid and pressure cook as directed.
After the pressure is released, remove the lid. Take the steamer basket out carefully.
Stir in tamarind concentrate and sugar (if adding). Using the back of a ladle or potato masher, mash the lentils to your desired consistency. Now add the steamed vegetables and check for seasoning. Let the curry rest for 2-3 minutes. Garnish with cilantro and serve.
Use the amount of sambar powder for a medium spice level. Or adjust the amount of sambar powder to reach your desired level of spiciness. Use 2 teaspoons for mild or increase to 1 ½ Tablespoons for spicy.
Add sugar or jaggery for a sweet-and-sour kick. Although completely optional, I highly recommend adding a touch of sugar or jaggery (unrefined sugar made from sugar cane or palm) to offset the tamarind's sour flavor.
Use a mix of vegetables when in season. Feel free to use any mix of 2 cups chopped vegetables such as pumpkin, green beans, eggplant, okra, potatoes or even Indian drumsticks (moringa) depending on the season.
Store leftovers in the fridge or freezer. The lentil and vegetable soup is best stored in an airtight container in the fridge for up to 4 days. Freeze into two plastic freezer storage bags or individual serving sizes for up to 1 month instead.
Note: The nutrition facts below are my estimates. If you are following any diet plan, I recommend cross-checking with your preferred nutrition calculator.