In a heavy medium-size saucepan, melt butter over lowest possible setting.
Cook 45 minutes to 1 hour or until butterfat separates from milk solids and milk solids turn golden-brown.
Watch carefully; occasionally gently skim through browned milk solids to be sure they are not burning.
When milk solids have sunk to bottom, strain clear butterfat through a fine strainer lined with several layers of cheesecloth into a container.
Cover tightly and store in refrigerator or a cool place 3 to 4 weeks.