Heat the oil in a large pot over medium heat. Add the chopped onions and cook until soft and lightly golden.
Stir in the minced garlic and grated ginger. Cook for one minute until fragrant.
Add the lamb chunks and brown them on all sides.
Sprinkle in the cumin, coriander, turmeric, and garam masala. Stir to coat the meat evenly.
Pour in the broth and bring the mixture to a simmer. Cover and cook for 45 minutes until the lamb is tender.
While the stew simmers, drain the soaked cashews. Blend them with the yogurt and the seeds from the cardamom pods until smooth.
Stir the cashew mixture into the pot along with the heavy cream. Simmer uncovered for 10 more minutes until the gravy thickens. Season with salt to taste.
Serve hot, topped with chopped cilantro and extra toasted cashews.