In a medium-sized bowl, add in the yogurt, garam masala, turmeric, cumin, fenugreek, coriander, chili powder, and cayenne pepper. Stir to combine until yogurt and spice mixture is mixed through. Add in the bite-sized chicken thighs and stir until all chicken pieces are coated with the yogurt mixture. Let marinate in the refrigerator overnight if possible, up to 24 hours ahead. If cooking right away, set aside.

In a large dutch oven or pot (minimum 4.5+ qt capacity), heat up the olive oil on low-medium heat. Add in the onion, garlic, and ginger. Turn up to medium heat and saute until onions are mostly clear (~5-10 minutes).

Add in the chicken and yogurt mixture, salt, and pepper. Stirring occasionally, cook until chicken is mostly cooked through (~5-10 minutes).

Stir in the tomato paste, crushed tomatoes, chicken broth, heavy cream, and sugar. Bring to a slow boil and turn down to a simmer for 15-20 minutes to let flavors combine. At this point, salt and pepper to taste. If needed, can add more sugar or cayenne pepper as well. Make sure to stir so nothing burns or sticks to the bottom of the pot!

Add in the butter a few minute before serving. For a richer and more traditional flavor, add the full 8 tbsp of butter. If a healthier curry is desired, still use at least 4 tbsp of butter for flavor. Stir the butter until completely melted and evenly distributed.

Serve over fresh naan or rice!