1. In a large bowl whisk together the yogurt, half of the minced garlic, half of the grated ginger, 1 teaspoon of the salt, 1/2 teaspoon of the black pepper, and 1 teaspoon each of the ground cumin and ground coriander.

2. Add the lamb cubes to the bowl and toss until every piece is well coated in the yogurt mixture. Cover and refrigerate for at least 30 minutes and up to 8 hours to tenderize and flavor the meat.

3. When ready to cook heat 2 tablespoons of the oil or ghee in a large heavy bottomed pot or Dutch oven over medium high heat. Shake excess marinade from the lamb and brown the pieces in batches until well seared on all sides, transferring them to a plate as they brown.

4. Reduce the heat to medium and add the remaining tablespoon of oil or ghee to the pot if needed. Add the diced onion and a pinch of salt and cook, stirring often, until the onion is very soft and golden brown, about 8 to 10 minutes.

5. Stir in the remaining garlic and ginger and cook for 1 minute until fragrant, then add the remaining 1 teaspoon cumin, 1 teaspoon coriander, the turmeric, paprika or mild chili powder, cayenne, cardamom, and cinnamon. Cook the spices for 1 minute, stirring constantly, to lightly toast them.

6. Add the tomato paste and cook, stirring, until it darkens slightly, 1 to 2 minutes. Pour in the crushed tomatoes and scrape up any browned bits from the bottom of the pot so they blend into the sauce.

7. Add the bay leaf and 1 cup of the broth, stirring to make a smooth sauce. Return the browned lamb and any accumulated juices to the pot, then add enough additional broth to just cover the meat.

8. Bring the curry to a gentle simmer, then reduce the heat to low and partially cover the pot. Simmer for 60 to 75 minutes, stirring occasionally, until the lamb is very tender and the sauce has thickened and reduced. If the sauce becomes too thick add a splash of broth or water as it cooks.

9. When the lamb is tender stir in the garam masala and simmer for 5 more minutes. Remove the bay leaf and any whole cardamom pods or the cinnamon stick if used.

10. Stir in the lemon juice and remaining 1/2 teaspoon salt and 1/2 teaspoon black pepper, adjusting to taste. If you prefer a looser sauce add a bit more broth; for a thicker curry simmer uncovered for a few additional minutes.

11. Just before serving stir in the chopped cilantro and mint if using. Serve the lamb curry hot over basmati rice or with warm naan, garnishing with extra herbs on top.