Make the marinade: in a large bowl combine the Plain Yogurt with the Lemon Juice, Ginger-Garlic Paste, Kashmiri Chili Powder, Ground Turmeric, Garam Masala and Fine Salt. Add the Chicken Thighs, toss to coat thoroughly, cover and refrigerate for at least 1 hour or up to overnight.
When ready to cook, heat a tablespoon of Neutral Oil in a heavy skillet over medium-high heat. Remove excess marinade from the chicken, then sear the thighs in batches (do not crowd the pan) until golden on both sides, 3–4 minutes per side; they should be browned but not fully cooked through. Transfer seared pieces to a plate and set aside.
Wipe the pan if it’s too crowded, reduce heat to medium and add a generous knob of Unsalted Butter. Once it melts, add the whole spices — Green Cardamom, Cinnamon Stick, Cloves and Bay Leaf — and cook for 30–45 seconds until aromatic.
Stir in another spoonful of the reserved ginger-garlic flavor from the marinade if desired, then add chopped or puréed Ripe Tomatoes to the pan. Simmer gently, stirring occasionally, until the tomatoes break down and the oil separates from the sauce, about 12–15 minutes. Taste and adjust heat with an extra pinch of Kashmiri Chili Powder if needed and balance with Sugar and a little more Fine Salt.
If you prefer a silky sauce, blend the tomato mixture until smooth (careful with hot liquid) and return it to the pan. Add a splash of Water to reach your desired consistency, then nestle the seared chicken into the sauce.
Cover and simmer over low heat until the chicken is cooked through and tender, about 12–18 minutes depending on piece size. Uncover, stir in the Heavy Cream and sprinkle in the Dried Fenugreek Leaves; simmer 2–3 more minutes so the flavors marry and the sauce becomes glossy.
Finish the curry with an extra small pat of Unsalted Butter if you like, taste and adjust seasoning, then scatter chopped Coriander Leaves over the top. Serve hot with steamed rice or warm flatbreads.
