In a large bowl, whisk together the Greek yogurt, lemon juice, garlic, ginger, garam masala, cumin, turmeric, coriander, smoked paprika, cayenne, salt, and pepper. Add in the chicken pieces, ensuring they are well-coated. Let them marinate for at least 15 minutes while you prepare other ingredients.

Heat 2 tablespoons of butter in a large skillet over medium heat. Add the marinated chicken, cooking until golden brown and cooked through, about 7-10 minutes. Make sure each piece is no longer pink in the center.

In the same skillet, add the diced yellow onions and sauté for about 5 minutes until they’re soft and translucent. Stir in the additional garam masala, cumin, and turmeric, letting the spices bloom for about a minute until fragrant.

Pour in the tomato sauce, stirring until well combined. Allow the mixture to simmer uncovered for about 5-7 minutes until it thickens slightly, stirring occasionally.

Reduce heat to low and gently fold in the room temperature half-and-half or cream and the additional plain Greek yogurt. Mix until fully incorporated, then bring to a gentle simmer for 3-5 minutes to heat through.

Once the sauce is velvety and creamy, remove from heat. Garnish with chopped cilantro and serve hot with fluffy rice or warm naan to soak up all that delicious sauce.