Marinate the chicken by tossing the thigh pieces with 1 teaspoon salt, garlic powder, paprika, ½ teaspoon curry powder, and Greek yogurt. Let rest for 10 to 15 minutes.

Heat 2 tablespoons of vegetable oil in a large skillet over medium-high heat. Add the chicken in a single layer and brown for 2 to 3 minutes per side until golden but not fully cooked. Remove the chicken to a plate.

Reduce heat to medium. Add the remaining tablespoon of oil and 1 tablespoon of butter to the skillet. Sauté the diced onion until soft and translucent, about 5 minutes, then add minced garlic and cook for 30 seconds.

Pour in the tomato sauce and stir. Add the sugar, 1 teaspoon salt, black pepper, and the remaining ½ teaspoon curry powder. Allow the sauce to simmer gently for about 3 to 4 minutes.

Return the browned chicken to the skillet and pour the heavy cream over everything. Stir to combine, and if desired, add ½ teaspoon cayenne. Reduce to low and simmer for 8 to 12 minutes until the chicken reaches 165°F (74°C) and the sauce thickens slightly.

Remove the skillet from the heat and stir in the remaining butter and garam masala. Adjust seasoning with salt or sugar if needed, and garnish with chopped parsley or cilantro if using.

Serve the butter chicken over steamed rice or tuck it into warm naan. Garnish with extra herbs and a squeeze of lemon if desired.