While the potatoes are baking, make the gravy.**** Place the onion, chilies, ginger, and garlic in a large food processor and blitz until smooth, scraping down the sides as needed. Transfer the puree to a bowl and set it aside.
1 yellow onion, 3-4 green chilies, 1 (1-inch) knob ginger, 4 cloves garlic
Pour the neutral oil into a large deep skillet and place over medium heat. Once the oil is shimmering, add the cinnamon stick, bay leaves, cardamom pods, and whole cumin seeds. Sauté until the cumin seeds pop and become fragrant. About 2 minutes.
¼ cup neutral oil, 1 cinnamon stick, 2 bay leaves, 4 green cardamom pods, 1 tsp whole cumin seeds
Add the puree to the pan along with a sprinkle of salt. Reduce the heat and sweat the onions. Once your onion puree starts to turn a soft golden color, add a can of whole tomatoes. Break the tomatoes up roughly with your spoon. Add the water to the can the tomatoes came in and give it a swirl. Add the water to the pan. Increase the heat and bring the mixture to a spirited simmer.
1 can whole tomatoes, 1 cup water
Stir in the whole unsalted cashews followed by the demerara sugar, salt, Kashmiri chili, garam masala, and ground coriander. Give the mixture a stir and reduce to a simmer. Cover and let cook for 15-20 minutes.
¼ cup whole unsalted roasted cashews, 1 tsp demerara sugar**, 1 tsp Kashmiri chili powder, ½ tsp kosher salt, ½ tsp garam masala, ¼ tsp ground coriander
Once the 15 minutes have passed, remove the cinnamon stick, bay leaves, and cardamom pods. Transfer the gravy to a large food processor and blitz until smooth. Pour the gravy back into the skillet using a fine mesh strainer. Use a rubber spatula to work as much of the gravy through as possible. This will result in a smoother tomato gravy but it does take some time. This step is optional.
Once the gravy is back in the skillet bring it back up to temperature. Stir in the cream and simmer for pan an additional 5 minutes to thicken.
¼ cup heavy cream