Sprinkle the chicken evenly on both sides with the cumin, coriander, and salt. Pour the yogurt over the chicken, and turn to coat. Marinate the chicken for 30 minutes, up to 4 hours.

Preheat the broiler and arrange the oven rack 8 inches or so from the broiler. Place tin foil in a baking sheet, and a baking rack over the tin foil. Place the chicken on the rack, and broil for 15 minutes or so, turning once halfway through, until the chicken is blistered and slightly charred in places.

Remove the chicken from the oven and let rest. When slightly cool, tear into large chunks with your fingers or two forks.

Add a pat of butter or a drizzle to a large skillet over medium heat. Add the onion and let cook for 1 minute. Add the chili pepper and let cook for 3 more minutes until veggies are just starting to soften - and sizzle.

Add the ginger, garlic, and garam masala to the veggies. Stir to coat, and let the veggies and spices toast for 1 minute until fragrant.

Add the tomatoes to the veggie mixture. Stir to warm through, then add the chicken and heavy cream. Taste the curry, and add more salt if you'd like. Let the curry simmer for 20 - 30 minutes, then serve as desired.