Combine the yogurt, lemon juice, ginger, garlic, garam masala, cumin, coriander, turmeric, paprika, and salt in a bowl. Add the chicken and stir until every piece is coated, then cover and marinate for at least 30 minutes or refrigerate overnight.

Heat the oil and 1 tablespoon of the butter in a large skillet over medium-high heat. Brown the chicken in batches for 2–3 minutes per side, then transfer it to a plate; it does not need to be fully cooked yet.

Reduce the heat to medium and add the remaining butter. Cook the chopped onion for 5–7 minutes, stirring occasionally, until soft and lightly golden.

Add the sauce garlic, ginger, garam masala, cumin, coriander, and paprika. Stir constantly for about 30 seconds, just until the spices and aromatics smell fragrant.

Pour in the crushed tomatoes and water or stock, then add the optional sugar and salt. Simmer uncovered for 10–15 minutes, stirring occasionally, until the tomato mixture has thickened slightly.

For a smooth restaurant-style sauce, blend the tomato mixture with an immersion blender until silky. Return the sauce to the skillet before adding the chicken.

Add the browned chicken and any juices from the plate to the sauce. Simmer gently for 8–12 minutes, until the chicken is cooked through and reaches 165°F/74°C internally.

Lower the heat and stir in the cream. Warm for 1–2 minutes without boiling, then stir in the optional final tablespoon of butter.

Taste the butter chicken and adjust the salt, chili, or sugar as needed. Garnish with cilantro and serve hot with basmati rice, naan, roti, lime wedges, or another favorite flatbread.