Mix yogurt, lemon juice, and half of the spices (cumin, garam masala, chili powder, turmeric, coriander, sweetener, and salt) in a large bowl. Stir until the mixture is smooth and well combined.

Add the chicken pieces to the marinade and coat evenly. Cover the bowl with plastic wrap and refrigerate for at least 3 hours to marinate.

Heat a large pan over medium heat and melt the butter. Add the chopped garlic and the remaining spices. Sauté for about 1 minute, stirring constantly, until the garlic is fragrant and the spices release their aroma. Stir in the tomato paste and continue to cook for another minute, mixing well to incorporate it into the spice mixture.

Pour in the heavy cream and stir continuously until the sauce becomes smooth and uniform in color.

If the sauce is too thick, add a little water or more cream to reach the desired consistency.

Add the marinated chicken along with any remaining marinade into the pan. Stir well to coat the chicken with the sauce.

Cook for 20-25 minutes over medium-low heat, stirring occasionally. Ensure the chicken is fully cooked and tender, and the sauce has thickened to a rich, creamy consistency. Adjust seasoning if needed.

Serve hot with cauliflower rice, fresh cilantro, extra cream, and chili flakes for garnish.