Melt the butter in a heavy saucepan over moderate heat. Increase the heat and bring the butter to a boil. When the surface is completely covered with foam stir the butter gently and reduce the heat to the lowest possible setting. Simmer uncovered and undisturbed for 45 minutes, or until the milk solids in the bottom of the pan have turned golden brown and the butter on top is transparent. Strain the butter through a sieve lined with linen or four layers of cheesecloth. If there are any solids in the ghee, no matter how small, strain it again until it is perfectly clear. Pour the ghee into a glass jar and seal tightly. This recipe makes about 1+1/2 cups, and may be kept at room temperature for several months, or almost indefinitely refrigerated. It will congeal if refrigerated, and so must be warmed before using if liquid ghee is called for.