Step 1

Place the cashews in a small heatproof bowl. Cover with boiling water and let soak 30 minutes, then drain.

Step 2

Meanwhile, season the chicken with salt, pepper, 1 teaspoon garam masala and 1/2 teaspoon turmeric. Heat 2 tablespoons vegetable oil in a large Dutch oven over high heat. Add the chicken in a single layer and brown 3 to 4 minutes per side. Remove to a plate.

Step 3

Reduce the heat to medium high and add the remaining 2 tablespoons vegetable oil to the pot. Add the onions, season with 1/2 teaspoon salt and cook, stirring, until soft and browned, 8 to 10 minutes. Add the ginger and garlic and cook, stirring, until golden, about 2 minutes. Add the coriander, cumin, chili powder and remaining 1/2 teaspoon turmeric; cook, stirring and scraping the pot, until the spices are toasted, about 30 seconds.

Step 4

Add the tomatoes and tomato paste to the pot. Cook, stirring, until the tomatoes break down, 4 to 5 minutes. Transfer the onion-tomato mixture to a blender (reserve the pot). Add the soaked cashews and 1 1/4 cups water and puree until smooth. Pour the sauce into the reserved pot.

Step 5

Return the chicken and any juices from the plate to the pot. Reduce the heat to medium low, cover and simmer, stirring occasionally to prevent sticking, until the chicken is tender, about 40 minutes.

Step 6

Stir in the heavy cream, butter, sugar and remaining 1/2 teaspoon garam masala. Thin the curry with water, if necessary; season with salt. Serve with rice and top with cilantro.