Combine all the marinade ingredients in a glass bowl. Toss to combine, cover and refrigerate up to 24 hours.: You will notice a smooth, pale mixture when the Greek yogurt , lemon juice , ground turmeric , garam masala , ground cumin , minced garlic , and grated ginger are fully integrated, and the marinade should coat each piece of chicken evenly. The aroma will be tangy and warm with spice notes rising from the bowl, a sign the acid and aromatics are interacting. Covering it and chilling allows the flavors to seep into the meat, which makes the texture tender and the flavor more cohesive. A common mistake is skimping on time, which leads to less flavored and firmer meat; if you are short on time, let it marinate at least 30 minutes, but overnight yields the best depth.
Heat 1/2 tablespoon of butter and the vegetable oil in a large non-stick skillet over medium heat. Add the onion and sauté until softened, about 3 minutes. Add the garlic and ginger and cook, stirring constantly for about 1 minute or until fragrant. Add the garam masala, chili powder, cayenne and salt. Stir and cook until fragrant, about 30 seconds. Increase the heat to medium-high and add the marinated chicken pieces. Don’t worry about scraping out any remaining marinade mixture - just discard. Sauté until the chicken is no longer pink on the outside, about 5 minutes.: When the butter melts into the oil you should see a gentle shimmer across the pan, that indicates the pan is hot enough. As the diced onion softens the kitchen fills with a sweet savory scent, and when you add the minced garlic and grated ginger there’s a bright, peppery perfume that tells you they are cooking properly. Toasting the spices for about 30 seconds releases their essential oils and transforms them from flat powders into aromatic boosters, so pay attention and stir continuously to avoid burning. When you add the marinated chicken , it should hit the pan with a distinct sizzle, searing and locking in juices; watch for edges to turn opaque and slightly golden. A frequent error is crowding the pan, which causes steaming rather than sautéing; if your skillet is compact, cook the chicken in batches to preserve a nice sear.
Add the tomato sauce and tomato paste and simmer uncovered for 15 to 20 minutes, stirring occasionally until the chicken is cooked through. Reduce the heat, and add the half-and-half and remaining tablespoon of butter, and warm gently until the butter is melted. Remove from the heat.: As the tomato sauce and tomato paste combine with the browned bits from the pan you will see the sauce go from a bright raw red to a deeper, richer hue, and small bubbles will appear at the edges as it simmers. The aroma becomes rounder and more complete as acids mellow and sugars develop; stirring occasionally prevents sticking and ensures even cooking. After 15 to 20 minutes the chicken should be cooked all the way through and tender; internal texture should feel firm but yielding. Reducing the heat before adding the half and half cream prevents it from splitting, and warming gently allows the sauce to emulsify into a glossy finish. Finish with the last tablespoon of butter for sheen. An easy oversight is rushing the simmer; under simmering leaves a thin, underdeveloped sauce while over-simmering can dry the chicken .
Serve over hot rice and garnish with chopped cilantro if desired.: The final presentation is all about contrast, place the warm curry over steaming rice so each spoonful carries sauce and texture together. The garnish of chopped fresh cilantro will contribute a bright herbal note and a pop of green that lifts the dish visually and in flavor. Listen for the small hiss as bowls are set down, and savor the glossy surface of the curry when you spoon it out. A common mistake is serving too cool; ensure everything is hot so the sauce is fluid and aromatic. If you need to rewarm, do so gently on low heat with a splash of water to loosen the sauce without breaking the emulsion.