Melt the butter over medium heat (do not let it boil). Pour the melted butter into a 2-cup capacity measuring cup. Allow the butter to sit for a few minutes to separate. There will be foam on the top, yellow clarified butter in the middle, and milk solids in the bottom. Skim and discard the foam from the top. Carefully pour only the clarified butter into a small container. Discard the milk solids.

Add the lemon zest to the butter and let it set out at room temperature for several hours for the lemon flavor to infuse into the butter. It will solidify. Store covered in the refrigerator for up to 3 weeks.

When ready to use, warm the butter over low heat in a saucepan. Strain to remove the lemon zest.

Caution: Do not use the microwave to warm the clarified butter.