Begin by washing and soaking the yellow mung lentils in excess water. While the lentils soak, you can prepare the ingredients- chop the different vegetables, measure the spices etc.
In a cooking pot (3 qt), heat up oil on medium heat. Add the bayleaf and green cardamom to the hot oil.
Next, add the chopped ginger, garlic, cilantro stems and green chilies to the oil. Fry for a minute or so untill you smell a nice aroma.
Next, add the onions into the pot. Lightly brown for 3-4 minutes until they appear soft and translucent.
Add the chopped tomatoes, beetroot pieces and soaked & drained lentils next to the pot. Sprinkle red chili powder and salt.
Saute the tomatoes for good 3-4 minutes on low medium heat with the aromatics till they begin to soften.
Pour hot water over the tomatoes and on low medium flame, bring to a boil. Reduce the heat to low, cover and let cook for 18-22 minutes or until the tomatoes, vegetables and lentils are soft.
Open the lid, pick and discard the bay leaf and green cardamom. Let the tomato mixture cool slightly.
Add the tomato mixture to a blender jar and blend to smooth puree. You could also puree it with immersion blender.
Pour the blended tomato soup back to the cooking pot placed on low medium flame. At this point, add more water if you wish to thin out the soup further.
Mix in the butter, black pepper powder, sugar and lemon juice(if using).
Bring the soup to a slow boil and simmer for 2-3 minutes.
Ladle into serving bowls and garnish with more black pepper and butter if desired. You can also add some chaat masala for a salty kick. Garnish with chopped cilantro leaves and serve warm.