Curry Stand Chicken Tikka Masala Sauce

2 tablespoons ghee (clarified butter)
1 onion, finely chopped
4 cloves garlic, minced
1 tablespoon ground cumin
1 teaspoon salt
1 teaspoon ground ginger
1 teaspoon cayenne pepper
1/2 teaspoon ground cinnamon
1/4 teaspoon ground turmeric
1 (14 ounce) can tomato sauce
1 cup heavy whipping cream
2 teaspoons paprika
1 tablespoon white sugar
1 tablespoon vegetable oil
4 skinless, boneless chicken breast halves, cut into bite-size pieces
1/2 teaspoon curry powder
1/2 teaspoon salt, or to taste (optional)
1 teaspoon white sugar, or to taste (optional)

Heat ghee in a large skillet over medium heat and cook and stir onion until translucent, about 5 minutes. Stir in garlic; cook and stir just until fragrant, about 1 minute. Stir cumin, 1 teaspoon salt, ginger, cayenne pepper, cinnamon, and turmeric into the onion mixture; fry until fragrant, about 2 minutes.
Stir tomato sauce into the onion and spice mixture, bring to a boil, and reduce heat to low. Simmer sauce for 10 minutes, then mix in cream, paprika, and 1 tablespoon sugar. Bring sauce back to a simmer and cook, stirring often, until sauce is thickened, 10 to 15 minutes.
Heat vegetable oil in a separate skillet over medium heat. Stir chicken into the hot oil, sprinkle with curry powder, and sear chicken until lightly browned but still pink inside, about 3 minutes; stir often. Transfer chicken and any pan juices into the sauce. Simmer chicken in sauce until no longer pink, about 30 minutes; adjust salt and sugar to taste.