thinly slice onions and mix it well with little salt. set it aside for 5 minutes and deep fry them in oil or bake them. stir/toss in between so that all sides are evenly browned.
Take the clean mutton pieces in a bowl, Put in all the items for marination along with brown onions and mix well so that its evenly coated. Close the bowl with lid and refrigerate overnight.
take out mutton and Once it is at room temperature, heat oil+butter in a pan, crackle cumin seeds, fennel seeds, bay leaves, cinnamon, cloves and cardamom.
after a minute, put in the marinated mutton. sprinkle very little water, close and cook in simmer until mutton is cooked and oil oozes out.