In a mixing bowl, combine chicken thighs with salt, garlic powder, paprika, curry powder, and Greek yogurt. Toss until coated and marinate for at least 15 minutes.

Heat a skillet over medium-high heat. Add half of the butter and a drizzle of oil. Add marinated chicken and sear for 4-5 minutes on each side until golden, then remove from skillet.

In the same skillet, add more butter if needed and sauté chopped onion until translucent (about 3-4 minutes). Stir in minced garlic for 1 minute, then add tomato sauce, sugar, salt, black pepper, curry powder, and optional cayenne. Simmer gently.

Lower the heat and stir in the heavy cream gradually. Let it simmer for 5-7 minutes until the sauce thickens.

Return the chicken with any juices to the skillet. Add garam masala and simmer for another 8-10 minutes until fully cooked.

Garnish with parsley or cilantro and serve warm with basmati rice or naan.