In a medium bowl, prepare the marination by combining the chicken, yogurt, lemon juice, garlic, ginger, chili powder, salt and turmeric. Allow the chicken to marinate for at least 30 minutes (preferably overnight).
Heat a large skillet on medium heat and add oil. Once the oil is heated, add the chicken pieces and cook for 5-6 minutes until lightly browned. Transfer the cooked chicken pieces to a plate and set them aside.
To the same skillet, add the butter to make tikka masala. Add the onion, garlic and garlic, saute for 3-5 minutes until the onions turn translucent.
Add in the spices; coriander powder, red chili powder, garam masala, cumin, salt, and turmeric powder. Saute for a minute.
Stir in the tomato paste and diced tomatoes and cook for 4-5 minutes. Once the sauce is thickened, add the heavy cream and cook for 5 more minutes. Add the brown sugar at this stage.
Once the tikka masala starts bubbling, add the chicken back to the pot and allow the masala to simmer for 10 minutes on a low flame.
Once the chicken is cooked through, add in the chopped cilantro and turn off the heat.
Serve the chicken tikka masala with a bowl of rice and lemon wedges on the side to enjoy!