Prepare the chicken marinade: In a medium bowl, combine the plain yogurt, lemon juice, 1 tbsp garam masala, cumin, coriander, turmeric, cayenne pepper, 1 tsp salt, and 1 tbsp vegetable oil or ghee. Mix well to create a smooth marinade.

Add the cubed chicken to the marinade. Toss to ensure each piece is thoroughly coated. Cover the bowl with plastic wrap and refrigerate for at least 1 hour, or ideally for 4-6 hours (or overnight) to allow the flavors to meld and the chicken to tenderize.

Preheat your broiler or grill to medium-high heat (approximately 200°C or 400°F). Thread the marinated chicken pieces onto skewers if using a grill, or arrange them in a single layer on a baking sheet lined with parchment paper if broiling. Discard any excess marinade.

Cook the chicken: Broil or grill the chicken for 8-12 minutes, flipping halfway through, until it's cooked through, slightly charred on the edges, and has a beautiful golden-brown color. Be careful not to overcook, as it will continue to cook in the sauce.

While the chicken is cooking or resting, start the sauce. In a large skillet or Dutch oven, heat 2 tbsp ghee or unsalted butter over medium heat. Add the finely chopped onion and sauté until softened and translucent, about 5-7 minutes.

Add the minced garlic and grated ginger to the skillet. Cook for another 1-2 minutes until fragrant, stirring constantly to prevent burning.

Stir in the tomato paste and cook for 1 minute, stirring constantly. This helps to deepen the flavor of the tomato paste.

Pour in the crushed tomatoes, 1/2 cup water, the remaining 1 tbsp garam masala, 1 tsp salt, and the optional sugar. Stir everything together well. Bring the sauce to a simmer, then reduce the heat to low, cover, and let it cook for at least 15-20 minutes, stirring occasionally, allowing the flavors to meld.

Once the sauce has simmered and thickened slightly, stir in the heavy cream or coconut cream. Continue to cook gently for another 5 minutes, stirring until the sauce is smooth and creamy. Do not boil after adding the cream, as it can curdle.

Add the cooked chicken pieces to the sauce. Stir gently to coat the chicken evenly. Let the chicken simmer in the sauce for another 5-10 minutes, allowing it to heat through and absorb the flavors of the masala.

Taste the sauce and adjust seasoning if necessary, adding more salt, garam masala, or a pinch of sugar if needed.

Serve the Chicken Tikka Masala hot, garnished with fresh chopped cilantro. It pairs perfectly with basmati rice, naan bread, or roti.