Step 1Melt butter in a large heavy-bottomed pot or Dutch oven over medium heat. Stir in onion and 1/2 teaspoon salt; cook until golden and browned around the edges, stirring occasionally, about 20 minutes. (Don’t be tempted to turn the heat up to medium-high; keeping the heat on medium ensures even browning without burning the butter.) Step 2Stir in garlic and ginger, and cook another 1 minute. Stir in cumin, paprika, garam masala and cinnamon stick, and cook another 30 seconds. Step 3Add tomatoes with their juices. Using a large spoon or flat spatula, break up and smash the tomatoes in the pot (or you can use a pair of kitchen shears to cut the tomatoes while they are still in the can). Stir in coconut milk and the remaining 1 teaspoon salt. Bring to a simmer, and continue to cook for 10 minutes, stirring occasionally, and continuing to mash up the tomatoes if necessary to help them break down. Step 4Stir in chickpeas and a pinch of cayenne if you like. Bring the pot back up to a simmer and cook, stirring occasionally, for another 10 minutes. Taste and add more salt if necessary. Step 5Serve spooned over white rice, and topped with cilantro.