Cut the chicken into bite-size pieces and sprinkle with salt, pepper, curry powder, Garam Masala, and sugar. Place it in a bowl or Ziplock bag.
Pour the yogurt over the chicken making sure to cover each piece. Set the chicken aside until ready to cook.
Heat vegetable oil in a large skillet over medium heat. Once the oil is hot, add the chicken.
Cook until the chicken is lightly seared and not quite cooked through – still a soft pink in the center. Stir often. Turn off the heat when the chicken is still slightly pink inside.
Heat the butter and olive oil in a different large skillet over medium heat. Once the oil and butter are hot, add the diced onions.
Cook until translucent then add the minced garlic. Cook for 1 minute, or until the garlic becomes fragrant.
Add the cumin, salt, ginger, cinnamon, turmeric, cayenne pepper, Garam Masala, and paprika. Cook for 1-2 minutes.
Add the tomato sauce, reduce the heat to low, and let the sauce thicken for 10-15 minutes, stirring often.
Add the cream and sugar and bring the sauce to a low boil. Add the cooked chicken.
Keep the heat on low and simmer until the sauce thickens and the chicken is fully cooked, about 15-30 minutes more.
