If possible the turmeric, cardamom, nutmeg, and fenugreek should be fresh ground from seed, then toasted. If that is impractical, already-ground spices may be briefly toasted in a hot, dry skillet.
In heavy saucepan, heat the butter over moderate heat. Stir and turn the pieces so that they melt evenly. Do not allow thr melted butter to brown or bubble — lower heat if necessary.
As soon as all of the it is melted, increase the heat and quickly bring it to all to a bubbly butter boil. A mass of small bubble will form on the top. Stir in the "wet" ingredients: the garlic, ginger, and onion. Cook for a minute or two, then add the "dry" ingredients: the turmeric, cardamom, cinnamon, clove, nutmeg, and fenugreek. Reduce heat to a very low simmer.
Simmer on a very low heat for 30 minutes to 60 minutes. Do not stir. The milk solids should sink to the bottom of the pan. A clear butter liquid should float on top.
Carefully strain the liquid through a clean cloth (cheesecloth). Repeat as necessary to obtain a liquid that is clear and free of spices and milk solids.
Pour the niter kebbeh into a clean jar with an airtight cover. Keep in the refrigerator and use as needed. Niter Kebbeh will turn solidi when chilled. Will keep for three months.