Set up the double boiler. Fill a pot with about 1 inch of water and place a heatproof bowl on top, making sure the bowl isn't touching the water. Bring the water to a gentle boil.
Melt the butter. Add the butter to the heat-safe bowl and let it melt completely, stirring occasionally.
Skim the top. As the butter melts, milk proteins will rise to the surface. Gently skim this white foam off with a spoon and discard.
Remove and dry. Using an oven mitt, carefully remove the bowl from the double boiler. Wipe the bottom to remove any residual water.
Strain it. Line a strainer with paper towel, a cloth, coffee filter, or cheesecloth. Strain the liquid into a bowl, avoiding the watery, milky white layer at the bottom.
Transfer and store. Pour the clarified butter into an airtight container and refrigerate.