In a bowl, combine chicken with all of the ingredients for the chicken marinade; let marinate for 30 minutes (or overnight).
Heat half of the coconut oil in a large skillet or pot over medium-high heat. When sizzling, add chicken pieces in batches of two or three, making sure not to crowd the pan. Fry until browned for only 3 minutes on each side (you will finish cooking the chicken in the sauce). Remove chicken and set aside.
Heat another tablespoon of coconut oil in the same pan. Fry the onions until they start to sweat (about 6 minutes) while scraping up any browned bits stuck on the bottom of the pan. Deglaze with 2 to 3 tablespoons of chicken broth.
Add garlic and ginger and sauté for 1 minute until fragrant, then add ground coriander, cumin and garam masala. Let cook for about 30 seconds or until fragrant, while stirring often.
Add crushed tomatoes, chili powder and salt. Let simmer for about 10 minutes, stirring occasionally until sauce thickens and becomes a deep brownish-red color.
Remove from heat, and use a stick blender to puree until smooth.
Stir the psmf sour cream (or cream), stevia and crushed kasoori methi (or fenugreek leaves) through the sauce. Add the chicken with juices back into the pan and cook for another 10 minutes until chicken is cooked through and the sauce is thick and bubbling.
Meanwhile make the carnivore rice. Place the egg whites into a medium-sized bowl. Add the broth, tamari and fish sauce and whisk until well combined.
Pour the egg mixture into the skillet and cook until the mixture thickens and small curds form, while scraping the bottom of the pan and whisking to keep large curds from forming. (A whisk works well for this task.) This will take about 7 minutes. Place the carnivore rice onto a platter and top with the butter chicken. Garnish with chopped cilantro and serve.