Chicken marinated in spiced yogurt and seared hard to mimic tandoor char, simmered into a reduced tomato-butter sauce finished with cream and crushed kasuri methi - the fenugreek leaves are what tie the tomato and cream together into that signature restaurant flavor.
1.Whisk together the yogurt, lemon juice, half the garlic, half the ginger, turmeric, chili powder, 1 teaspoon of the garam masala, and salt; marinate the chicken in the mixture, covered, for at least 30 minutes, ideally overnight.
2.Sear the marinated chicken in a very hot pan or under the broiler until charred in spots - this mimics tandoor cooking and gives butter chicken its signature smoky edge; it doesn't need to be fully cooked through yet.
3.Melt the butter and sauté the onion with the remaining garlic and ginger until softened, then stir in the remaining garam masala and crushed tomatoes.
4.Simmer the tomato mixture uncovered for 15 minutes, stirring occasionally, until reduced and nearly dry - this concentrates the flavor before blending.
Blend the sauce until smooth, then return it to the pot with the cream, sugar, and seared chicken; simmer for 10 minutes until the chicken is cooked through.
6.Crush the kasuri methi between your palms and stir it in just before serving - it's what bridges the tomato and cream into the dish's signature flavor.