Combine the masoor lentils, water and turmeric.
Bring to a lively simmer uncovered. Uncovered is key. I've had lentils boil over on me more times than I can count. Now I start them uncovered. Problem solved.
Once the lentils come to a simmer, reduce heat to low and cover.
Cook lentils until they completely break down into a creamy consistency. You will not be able to discern individual lentils. This should take somewhere around 40 minutes.
Add the salt. You will adjust the seasoning at the end.
Heat the oil over medium heat.
Add the kashmiri chilies if using. Cook until the edged just start to bubble.
Flip the kashmiri chilies. Add the mustard seeds and cumin seed and fry briefly. They should crackle a bit and dance around.
Turn the heat down a bit and add onion. Cook until the onions are translucent.
Add the green chilies, curry leaves and methi and continue to cook for around 2 minutes.
Stir in the tomato paste or fresh tomatoes if using. Cook for 20-30 seconds then add the tarka to the dahl.
Stir to thoroughly combine.
Adjust consistency to your taste with little bit of water (I like it a bit runny).
Add the cilantro and lemon juice to taste.
Adjust salt. Around a half a tsp give or take. Creep up on it. You can add salt. You can't take it away.
