In a blender, combine the raw onion, garlic, ginger, chili, yogurt, and spices, and blend until smooth.
Pour the blended mixture over the lamb and mix thoroughly. You can marinate it overnight or proceed immediately.
In a pan, heat oil and butter until very hot.
Smash three black cardamom pods and add the crushed coriander seeds, stirring quickly.
Add the marinated lamb to the pan and sprinkle fried onions on top.
Cook the lamb until it starts to brown.
Add a splash of boiling water, cover the pan, reduce the heat to low, and let it simmer for up to an hour, stirring occasionally to avoid sticking.
If desired, reduce the cooking liquid to enhance the flavor, adding a little water if you want a saucier dish.
Chop fresh coriander and mix it into the finished lamb.
Serve the lamb with hot, fluffy buttered naan.
