In a large mixing bowl, combine Greek yogurt, garam masala, smoked paprika, ground cumin, minced garlic, minced ginger, and salt. Stir well to create a smooth marinade. Add the boneless chicken thighs to the bowl, ensuring they are fully coated. Cover and refrigerate for at least 1 hour; marinating overnight is recommended.

Heat a heavy-bottomed skillet over medium-high heat and drizzle in some oil. Once shimmering, add the marinated chicken pieces in batches, searing for about 5-7 minutes until browned. Remove and set aside.

In the same skillet, reduce heat to medium and add more oil if needed. Once hot, add diced onions, sautéing for about 5-6 minutes until golden and translucent.

Add minced garlic, minced ginger, ground cumin, and smoked paprika to the skillet. Stir and cook for another 1-2 minutes until fragrant.

Stir in the tomato puree, combining well with the sautéed onions and spices. Let simmer for about 5 minutes to thicken slightly.

Once thickened, pour sauce into a blender or use an immersion blender in the skillet. Blend until smooth and creamy.

Add seared chicken back into the skillet with the smooth sauce. Stir to coat thoroughly and let simmer on low heat for about 15 minutes.

After simmering, stir in heavy cream and let warm through for another 5 minutes.

Remove from heat and garnish with freshly chopped cilantro. Serve hot with basmati rice or warm naan.