Add dal, water, tomatoes, chopped onion, sugar, salt, turmeric, cayenne and sambhar spice blend to the inner liner of your Instant Pot.
Cook for 10 minutes at high pressure. Allow the pot to sit undisturbed for 10 minutes, and then release all remaining pressure.
Using an immersion blender, blend together the dal and vegetables. You are doing this to create a flavorful mix and to keep the dal from settling to the bottom in what will be a relatively thin broth.
Second Cooking Cycle:
To the blended dal mixture, add 2 cups water, the tamarind concentrate, and the frozen vegetables.
Cook for 2 minutes at high pressure and then immediately release all remaining pressure.
On the stovetop in a small pan (preferably a tadka ladle), heat 1 tablespoon of ghee. When it is hot, add mustard seeds, the whole red chilies, and the curry leaves. Stand back and allow the mustard seeds to splutter about 30 seconds.
Pour this hot, flavored ghee onto the sambhar, garnish with chopped cilantro and serve.
You can use ready-made sambhar masala for this recipe if you prefer
You can use other vegetables such as diced pumpkin, chopped eggplant, or whole okra as well