Begin by placing the chicken thighs in a large bowl. Sprinkle with salt, garlic powder, sweet paprika, curry powder, and add the Greek yogurt. Mix thoroughly until well-coated and let marinate for at least 15 minutes.

Heat 2 tablespoons of vegetable oil in a large skillet over medium-high heat. Add the marinated chicken and sear for about 8-10 minutes, until golden brown and cooked through. Remove chicken and set aside.

In the same skillet, reduce heat to medium and melt 2 tablespoons of butter. Add minced garlic and onion, sauté for about 3-4 minutes until onion is translucent.

Stir in 1 cup of tomato sauce and 1 teaspoon of sugar. Simmer for 2-3 minutes, then return the cooked chicken to skillet, followed by 1/2 cup of heavy cream. Stir until smooth.

Add cayenne pepper, garam masala, curry powder, and black pepper. Simmer on low heat for about 10 minutes, adjusting seasoning as necessary.

Stir in the remaining tablespoon of butter for richness; fold it in until melted. Simmer for an additional minute.

Serve the Homemade Butter Chicken hot, garnished with parsley or cilantro. Accompany with warm naan and rice.