Step 1
Place chicken in a bowl and drizzle vegetable oil over chicken; toss to coat.

Step 2
Whisk kosher salt, garam masala, ground cumin, ground coriander, smoked paprika, ground turmeric, black pepper, cayenne pepper, and cardamom together in a small bowl. Season chicken with spice mixture and turn to coat evenly.

Step 3
Melt clarified butter in a large, heavy skillet over high heat. Cook chicken thighs in hot butter until browned on all sides, 5 to 10 minutes. Transfer chicken to a plate. When cool enough to handle, cut chicken into bite-size pieces.

Step 4
Reduce heat under the skillet to medium-high. Stir onion into skillet; saute until onion softens and turns translucent, 5 to 6 minutes. Add tomato paste and stir. Saute until paste caramelizes, about 5 minutes. Stir garlic and ginger into tomato-onion mixture and cook until fragrant, about 1 minute.

Step 5
Pour the crushed tomatoes into the skillet and bring to a boil while scraping the browned bits of food off of the bottom of the skillet with a wooden spoon. Pour in coconut milk and chicken broth; bring to a simmer, reduce heat to medium low, and cook, stirring occasionally, until flavors blend and sauce is slightly reduced, about 15 minutes.

Step 6
Stir chicken, any accumulated juices from the chicken, cilantro, and red pepper flakes into tomato mixture; bring to a simmer, reduce heat to medium-low, and cook until chicken is cooked through and tender, 10 to 15 minutes. Season with salt and black pepper.