In a small bowl, whisk together the spices and seasonings. Set aside.
In a mixing bowl, whisk together 1 cup milk, lime juice, and 2 Tbsp. of the spice mixture.
Place the chicken thighs into a bowl and the milk mixture. Toss to coat and chill for 2-6 hours.
Melt the butter in a stock pot over medium heat. Add the diced onions and sauté until transparent.
Stir the remaining spice mixture into the onions and cook for two minutes. Add the tomato paste and cook two additional minutes.
Pulse the tomatoes (liquid included) in a blender and add them to the pot with ½ cup water. Season with salt and pepper, to taste.
Bring the sauce to a simmer and cook for 20 minutes.
Meanwhile, prepare a baking sheet with foil. Remove the chilled chicken from the milk mixture and place it on the prepared baking sheet. Broil the chicken for about 5 minutes on each side until slightly charred.
Stir remaining ½ cup milk into the sauce.
Remove the chicken from the oven and cut it into 2-inch pieces.
Place the chicken pieces in the pot. Simmer for 10 minutes until sauce is thickened and chicken is cooked through.
Serve over basmati or jasmine rice. Garnish with fresh cilantro leaves.