In a heavy saucepan, melt the butter over very low heat; so not stir.
When butter is completely melted, increase heat just enough to bring to boiling. Stir once and immediately reduce the heat to low. Simmer the butter, uncovered, for 30 minutes.
Line a strainer with several layers of clean cheesecloth. Strain the clear liquid through it, making sure none of the solids in the bottom of the pan goes through. Pour into a clean jar. Cover and label. Store in the refrigerator.