In a medium bowl, combine Greek yogurt, lemon juice, minced garlic, grated ginger, garam masala, cumin, smoked paprika, and salt. Add chicken thigh chunks, tossing to coat thoroughly. Marinate for 15 minutes at room temperature (or up to 4 hours refrigerated).

Heat 1 tablespoon of oil in a large heavy skillet or cast iron Dutch oven over high heat until shimmering. Remove chicken chunks from marinade, wiping off excess so it sears rather than steams. Sear chicken in batches for 3–4 minutes per side until deeply browned and blistered with appetizing charred spots. Transfer chicken to a clean plate (it does not need to be fully cooked through yet).

Melt butter in the same skillet over medium heat. Add diced onions and cook for 5 minutes until soft, sweet, and translucent. Stir in minced garlic and grated ginger, cooking for 1 minute until fragrant.

Add garam masala, cumin, ground coriander, and turmeric. Toast the spices in the butter for 45 seconds to release aromatic essential oils.

Pour in the pureed crushed tomatoes and brown sugar. Simmer uncovered over medium-low heat for 8 to 10 minutes, stirring occasionally, until the tomato sauce deepens into a rich brick-red color and thickens slightly.

Stir in heavy cream until the sauce transforms into a velvety, luminous orange masala sauce. Gently fold in the seared chicken pieces along with any accumulated flavorful juices from the plate.

Simmer gently on low heat for 5 minutes until chicken is completely tender and cooked through (165°F / 74°C internal temperature). Taste sauce and adjust salt as desired.

Ladle into serving bowls, swirl an extra drizzle of fresh cream on top, and scatter chopped cilantro. Serve piping hot with warm garlic naan and steamed basmati rice.