Heat 1 tablespoon oil in pot or Dutch oven. Place mushrooms and chestnuts in pot.
Saute over high heat for 3-4 minutes until the chestnuts and mushrooms are lightly browned. Remove to a plate before the mushrooms start to ooze out any of their juices.
In the same pot add a teaspoon of oil and the sliced onions.
Add salt and saute the onions over medium-low heat about 10 minutes until they are browned. If they start to stick, add a tablespoon of water at a time and scrape up any bits that stick with a ladle.
Add ginger garlic paste, ground cumin, ground cilantro, garam masala, turmeric and cayenne to the pot. Stir in tomato paste.
Add cilantro and mix well. Remove the mixture to a blender, add a cup of water and blend to a very smooth paste. Set aside. In the same pot, wiped clean or rinsed, add remaining oil. Add the chopped onions and salt and saute over medium heat for 2-3 minutes until translucent.
Stir in the blended paste and the roasted chestnuts and mushrooms. Add another cup of water and mix well. Bring to a boil, cover, and let the sauce simmer 10 minutes.
Stir in the coconut milk followed by the cilantro. You can thin out the sauce more with water if you want to. Check for salt, bring to a boil, then turn off heat. Serve hot.