In a large bowl, combine the chicken pieces with yogurt, garlic, ginger, korma curry paste, cumin, coriander, turmeric, cinnamon, cayenne pepper, and salt. Mix well to coat the chicken evenly. Cover and marinate in the refrigerator for at least 1 hour, or overnight for best flavor.
Heat the vegetable oil in a large skillet or Dutch oven over medium heat. Add the chopped onion and sauté until golden brown, about 8-10 minutes.
Add the marinated chicken mixture to the skillet, including all the marinade. Cook for about 5 minutes, stirring occasionally, until the chicken is browned.
Pour in the coconut milk and bring the mixture to a simmer. Reduce the heat to low, cover, and let it cook for 25-30 minutes, stirring occasionally, until the chicken is tender and the sauce has thickened.
Taste and adjust seasoning with additional salt or spices if needed.
Serve the chicken korma over cooked basmati rice and garnish with fresh cilantro.