In a large mixing bowl, whisk together the 1 cup plain whole-milk yogurt, 4 cloves garlic, 1 tbsp fresh ginger finely grated, 1 ½ tsp garam masala, 1 ½ tsp ground cumin, 1 tsp ground turmeric, chili powder, 1 tsp kosher salt, and 1 tbsp neutral oil. Add the 2 lb boneless skinless chicken thighs chunks and toss well to coat every piece. Cover and refrigerate for at least 1 hour, or ideally overnight for the deepest flavor.

When ready to cook, position an oven rack in the top position and set the broiler to high. Line a baking sheet with aluminum foil and place a wire rack on top. Arrange the marinated 2 lb boneless skinless chicken thighs pieces in a single layer on the wire rack, shaking off any excess marinade.

Broil the 2 lb boneless skinless chicken thighs for 10–12 minutes, flipping once halfway through, until the pieces are cooked through and have charred spots on the edges. The char is key — it adds the signature smoky flavor. Set aside.

While the 2 lb boneless skinless chicken thighs broils, melt the 2 tbsp unsalted butter with the 1 tbsp neutral oil in a large, deep skillet or Dutch oven over medium heat. Add the diced large yellow onion and cook, stirring occasionally, for 10–12 minutes until softened and lightly golden. Don't rush this step — well-cooked onions form the flavor base of the sauce.

Add the 4 cloves garlic and 1 tbsp fresh ginger finely grated to the onions and cook for 2 minutes, stirring constantly, until fragrant. Then add the 1 ½ tsp garam masala, 1 ½ tsp ground cumin, 2 tsp ground coriander, chili powder, and 1 tsp ground turmeric. Stir and cook the spices for 1–2 minutes until they smell deeply aromatic and begin to stick to the pan slightly.

Add the 1 tbsp tomato paste and stir it into the spiced onions. Cook for 2 minutes, letting it caramelize slightly. Pour in the 1 can crushed tomatoes and 1 tsp kosher salt, stir everything together, and bring to a simmer. Cook uncovered for 15 minutes, stirring occasionally, until the sauce has thickened and darkened in color.

Reduce the heat to low and stir in the 1 cup heavy cream. Taste the sauce and adjust 1 tsp kosher salt as needed. If the 1 can crushed tomatoes are quite acidic, stir in the 1 tsp granulated sugar to balance acidity to balance. Let the sauce simmer gently for 5 minutes.

Add the broiled 2 lb boneless skinless chicken thighs pieces (along with any resting juices from the pan) into the sauce. Stir gently to coat all the chicken, then simmer together for 5–8 minutes over low heat so the 2 lb boneless skinless chicken thighs absorbs the sauce flavors.

Ladle into bowls or a serving dish. Drizzle with a swirl of heavy cream and scatter fresh fresh cilantro roughly chopped over the top. Serve immediately with basmati rice, naan, or both.