I use a crockpot. Put the butter (up to eight pounds fits in mine) in, cover, and set the temperature setting to "low."
Let the butter melt and simmer for about eight hours; at this point, there will be a sort of foamy "scum" on top (protein, mostly), a lot of butterfat (all the good yellow stuff) in the middle, and the milk solids at the bottom.
Skim off the scum. Slowly, carefully, and patiently (prepare to use choice words when you spill), pour the yellow ghee into a four-cup measuring cup, in batches. Then, pour slowly into jars, filtering through cheesecloth to catch any stray milk solids. Stop pouring when the milk solids start threatening to run into the containers.
Another way to store the ghee is to pour the liquid into a large, rectangular or square baking dish(es). Chill until mostly solid, then score and slice into whichever size bricks/sticks work for storage. Freeze in ziplock bags, or wrap in wax paper...
The milk solids are delicious, if you can eat them.
The ghee keeps for a long time in the fridge/freezer.
Depending on your butter, you get about 3/4 pound of ghee for every pound of butter you use.