Step 1: In a medium bowl, combine chicken chunks with 1 teaspoon salt, 1 teaspoon garlic powder, 1 teaspoon sweet paprika, ½ teaspoon curry powder, and 1 tablespoon Greek yogurt. Mix well to ensure chicken is evenly coated. Cover the bowl and marinate in the refrigerator for at least 15 minutes, or up to 30 minutes for deeper flavor.
Step 2: Heat 3 tablespoons vegetable oil and 1 tablespoon of butter in a large skillet or Dutch oven over medium-high heat. Once hot, add the marinated chicken and cook for 5-7 minutes, turning occasionally, until lightly browned on all sides. The chicken does not need to be cooked through at this stage. Remove the chicken from the skillet and set aside.
Step 3: Reduce the heat to medium. Add the remaining 2 tablespoons of butter to the skillet. Once melted, add the minced garlic and diced onion. Sauté for 5-7 minutes until the onion is softened and translucent, stirring frequently.
Step 4: Stir in the 15-ounce can of tomato sauce, 1 teaspoon sugar, 1 teaspoon salt (adjust to taste), ½ teaspoon black pepper, ½ teaspoon cayenne pepper (if using for heat), and 1 teaspoon garam masala, and an additional ½ teaspoon curry powder. Bring the sauce to a gentle simmer, scraping any browned bits from the bottom of the pan.
Step 5: Return the cooked chicken to the skillet, immersing it in the sauce. Pour in the 2 cups of heavy cream. Stir well to combine all ingredients. Reduce the heat to low, cover the skillet, and let it simmer for 15-20 minutes, stirring occasionally, until the sauce has thickened slightly and the flavors have melded together.
Step 6: Taste the butter chicken and adjust seasoning if necessary, adding more salt or sugar as desired. Serve hot, garnished with fresh chopped parsley, if desired, and enjoy with rice or naan.