Heat 4 tbsp vegetable oil or butter in a pan over medium heat. Sauté 2–3 finely chopped garlic cloves until fragrant, then add finely chopped onion and cook until golden brown. Stir in 300g canned chopped tomatoes and simmer for 5 minutes until thickened. In a separate bowl, mix 1 sachet (50g) Butter Chicken spice mix with 100ml water to form a smooth paste, then add it to the pan and cook for 2 minutes. Add diced boneless chicken and cook for about 10 minutes until fully done. Stir in 250ml single cream and 2 tbsp butter, mix well, and simmer for 2–3 minutes until creamy. Season with salt and set aside.