Peel and roughly chop 4 large onions. Peel the thumb-sized piece of ginger and roughly chop. Peel the 8 garlic cloves. Place the chopped onions, garlic, ginger and ¼ cup hot water in a food processor or blender and blend to a thick, smooth paste. Transfer the paste to a bowl and set aside.

Peel the remaining 6 onions and slice them into half-moons. Set the sliced onions aside.

Heat a large heavy-bottomed pan over medium-high heat. Add 3 tablespoons ghee (or flavorless oil) and heat until shimmering.

Add all of the sliced onion half-moons to the pan. Fry on medium-high, stirring occasionally, until the onions are softened and caramelized (about 10–15 minutes). Use a slotted spoon to transfer the caramelized onions to a plate and reserve them.

Cut the 2.2 lb lamb into bite-size chunks. Add the lamb to the same pan and fry over medium-high heat, turning or stirring to brown all sides (about 6–8 minutes). Work in batches if necessary to avoid crowding.

Return the pan to low heat and add the onion-garlic-ginger purée to the browned lamb. Stir well to coat the lamb. Cook over low heat for 10 minutes, stirring occasionally, until the purée has softened; do not allow it to brown.

Stir in 1 tablespoon ground cumin, 1 tablespoon ground coriander, 1 teaspoon ground turmeric, a pinch of ground cinnamon, ½ teaspoon ground cardamom and ¼–½ teaspoon cayenne pepper (if using). Cook on low for 1 minute to bloom the spices.

Add 2 cups vegetable stock and 1 tablespoon tomato paste. Stir to combine, bring to a gentle simmer, then reduce heat and simmer uncovered for 1 hour, stirring occasionally, until the lamb is tender.

If the lamb is not tender after 1 hour, continue simmering for an additional 10–15 minutes, checking for doneness.

Stir the reserved caramelized onions, ½ cup plain yogurt or coconut cream, and ½ teaspoon garam masala into the curry. Cook on low for 5 minutes to heat through and meld the flavors.

Remove from the heat, squeeze the juice of ½ fresh lemon over the curry, and stir. Garnish with fresh cilantro before serving.