Preparing the Chicken Tikka:
In a mixing bowl, blend yogurt, garlic, ginger, garam masala, cumin, coriander, paprika, salt, oil, lemon juice, cayenne pepper, and black pepper until smooth. Add the chicken cubes and coat thoroughly. Cover and refrigerate for a minimum of 3 hours, ideally overnight.
Heat 1 tbsp oil in a non-stick skillet over high heat until it begins to smoke. Add half the marinated chicken, spread it out, and sear undisturbed for about 2 minutes until charred. Turn and cook the other side similarly. Transfer to a bowl. Repeat with the remaining chicken, adding more oil if necessary. Discard charred remnants from the pan.
Making the Sauce:
Wipe the skillet clean or use a medium pot. Heat the oil and butter over medium-high heat. Once the butter has melted, sauté the onions, ginger, and salt for about 5–7 minutes, stirring constantly until fragrant and lightly golden. Lower the heat to medium, add garlic and paprika, and stir for another 2 minutes.
Incorporate the spice mix—garam masala, coriander, turmeric, cumin, cayenne, and cardamom—and continue cooking for 2 more minutes. Add the passata and water, stir, bring to a gentle simmer, cover, and reduce the heat to low. Simmer for 15 minutes, stirring occasionally.
Transfer the sauce to a bowl and blend until smooth using a stick blender. Return to the pan, then stir in cream, sugar, and butter until the butter melts. Fold in the cooked chicken, and allow to simmer a few minutes until heated through and fully cooked. Optionally, finish with a sprinkle of garam masala.
Serving Suggestion:
Ladle over steamed basmati rice and garnish with fresh coriander if desired. Pairs beautifully with a quick no-yeast flatbread.