In a mixing bowl, combine chicken chunks with salt, garlic powder, sweet paprika, and curry powder. Add the Greek yogurt and mix thoroughly to ensure each piece is well coated. Allow the chicken to marinate for at least 15 minutes at room temperature.

Heat a large skillet over medium heat and add the vegetable oil and butter. Once the butter is melted and bubbling, add the marinated chicken to the pan. Cook for about 8-10 minutes, turning occasionally, until the chicken pieces are browned and fully cooked through, then remove them from the skillet and set aside.

In the same skillet, add the remaining butter. Once it melts, toss in minced garlic and diced onion, sautéing for about 3-4 minutes until the onion becomes translucent and fragrant.

Pour in the tomato sauce, followed by sugar, salt, black pepper, and cayenne pepper if desired. Stir to combine the mixture, then let it cook for about 5 minutes over medium heat.

Lower the heat and stir in the heavy cream, garam masala, and an additional teaspoon of curry powder. Mix well and let it simmer gently for about 5 minutes.

Return the cooked chicken to the skillet, ensuring each piece is well-coated in the sauce. Allow everything to simmer together for another 5-10 minutes.

If desired, garnish your Butter Chicken with freshly chopped parsley and serve hot with warm naan or steamed rice.