In a large bowl, add the lamb, turmeric powder, curry powder, Greek yogurt, and kosher salt. Mix well making sure all the pieces are well coated. Set aside and leave to marinate for 2 hours or overnight.
Heat pan on medium-high melt the butter and, then, add all the whole spices. As they start to make some noise (yes, listen to your food), add the onions. Sauté the onions until they turn light brown.
Add the garlic and ginger and sauté for a couple of minutes.
Add the powdered spices and cook for another two minutes.
Add the marinated lamb to the pan and blend with the spices and onions.
Add the tomato sauce and cook until the paste adheres to the lamb pieces.
Add the chicken stock and bring to a simmer. Cover the pan and cook for 60 minutes (stirring occasionally).