In a heavy-bottomed, medium saucepan, gently melt the butter over medium heat. Avoid letting it brown or burn.
Once melted, increase the heat to bring the butter to a boil. As soon as it boils, immediately reduce the heat to the lowest possible setting. A layer of white foam will form on top; carefully skim this off with a spoon and discard.
Allow the butter to simmer gently, uncovered, on the lowest heat for about 45 minutes.
Do not stir. During this time, the milk solids will sink to the bottom and turn a toasty golden brown, and the ghee will become clear and fragrant.
Remove the pan from the heat and let it cool for a few minutes.
Line a fine-mesh sieve with two layers of cheesecloth and place it over a clean, dry, heatproof storage jar.
Carefully pour the clear, golden liquid through the prepared sieve, leaving the browned milk solids behind in the pan. To ensure maximum purity and shelf life, you can strain it a second time.
Let the ghee cool to room temperature before sealing with a tight-fitting lid. It will keep for 2-3 months at room temperature or indefinitely in the refrigerator. Ghee will solidify and become opaque when chilled.