Cut the chicken thighs into bite-sized pieces, trim off any excess fat, and set them aside.
In a large bowl, whisk together the yogurt, garlic, ginger, garam masala, chili powder, fenugreek, garlic powder, cumin, onion powder, paprika, salt, and turmeric until smooth.
Add the chicken to the bowl, and toss it in the marinade. Cover with plastic wrap, and place it in the fridge for at least one hour to marinate or up to overnight if you can.
When ready to cook, place a dutch oven or a large skillet with deep sides over high heat. Once hot, add the ghee. Place the marinated chicken into the pot, and sear it the best you can, stirring occasionally. Cook the chicken for about 10 minutes or until it has browned on most sides.
Add the tomato passata, cream, sugar, salt, and any leftover marinade from the chicken to the pot with the chicken, and mix it all together. Scrape any browned bits off the bottom of the pot.
Bring the ingredients to a simmer, and lower the heat to medium-low. Cover and simmer for 30 minutes, stirring occasionally.
Serve warm with a garnish of fresh cilantro, if desired.