Melt butter in a large skillet over medium-low heat. Let it sputter and bubble until a fine foam covers the surface, about 20 minutes. Continue cooking, gently pushing foam covers aside with a spoon occasionally to check the color of the milk solids at the bottom of the skillet.
Once milk solids turn golden brown and butter just begins to smell nutty, about 20 minutes more, pour the butter through a cheesecloth-lined sieve into a medium bow.
Transfer ghee to a clean jar and let cool. Ghee will keep, tightly covered in the refrigerator, for up to 6 months.