Use a medium bowl to combine the tomato puree, cream, and lemon juice. Set aside
Heat a medium sized pot and add 2 Tablespoons of oil and the chopped onion. Cook, stirring until the onion softens
Add all of the spices and stir well while it is cooking. It may need a little extra oil if the mixture is very dry. Watch it doesn't burn
Add the garlic and ginger and sate for several minutes or until fragrant (you start to small it cooking). Take off the stove and cool slightly
Add the spice mix and the salt to the tomato mixture and stir well
Put the chicken into this mixture and turn to combine until well coated
Put in a single layer into the baking dish and cover with the sauce.
Bake uncovered for 40 minutes or up to an hour for large pieces. test that the chicken is fork tender and cooked through
Serve the Butter Chicken with raita (see the recipe), rice and popadums if you like