Marinate the chicken with garlic, salt, pepper, and spices, then sear in a hot skillet until golden and set aside. In the same skillet, sauté onions until soft, stir in the remaining spices, tomato purée, and let simmer. Add cream and butter to create a luscious sauce, then return the chicken and simmer until fully cooked and tender. Meanwhile, cook basmati rice until fluffy and warm the naan. Assemble your bowl with a scoop of rice, a generous serving of butter chicken, and naan on the side. Garnish with cilantro and a squeeze of lemon if desired.