In a small pot, melt butter over low heat until bubbling and foaming subsides. Remove from heat, let cool slightly (don’t let butter re-solidify), then skim any foam off the top.
Line a sieve with cheesecloth or a clean dish towel and place over a heat-safe bowl or container. Leaving the white milk solids at the bottom of the pot, carefully pour or spoon yellow butter fat through the sieve and into the container. Let cool completely before refrigerating for up to 1 month.