Place the butter in the inner pot of the slow cooker. Put the lid on, but make sure it is vented to release the steam as the butter cooks.
1 pound unsalted butter
Set the timer for 6-8 hours on high. 6 hours will produce ghee that has a mild nutty flavor, but leave it for 8 hours and the nuttiness is outstanding.
When the time is up, you should see an amber colored liquid with dark particles of milk fat settled on the bottom and sometimes the top of the liquid. The aroma should be sweet and nutty.
Place the strainer over a clean heatproof container or jar and line the strainer with the flour sack, cheesecloth, or a coffee filter. Pour the cooked butter through the strainer so the clear amber colored ghee goes into the glass jar and the milk fats are left in the strainer. Put the lid on the jar of ghee.
Allow the ghee to cool and discard the milk solids. Once the ghee has cooled, you will see it thicken up and lighten in color. This is completely normal. Store the ghee at room tempurature or in the refrigerator.
2 cups (1 pound) of butter will yield approximately 1½ cups of ghee. Tips for Making Slow Cooker Ghee
Make sure your slow cooker lid is vented. Part of the process of turning butter into ghee is evaporation and you need the water to be able to evaporate. Most slow cookers do have a little hole in the lid, but if yours does not then either keep the lid off and cover the top with a paper towel or dish cloth that will let the water evaporate or place a spoon between the top of the slow cooker insert and lid to vent it. When using your Instant Pot or Ninja Foodi with 2 lids, make sure the valve is vented to let the steam escape or leave the pressure lid off.
When at all possible, use a ceramic insert in your slow cooker, Instant Pot, or Ninja Foodi. The stainless steel inserts do conduct heat a little differently and you will want to check on the ghee every few hours as it cooks to make sure it is not getting hot enough to burn the milk solids.
Each slow cooker may cook a little differently, some hotter and faster than others. This recipe was tested in the Ninja Foodi Pressure Cooker & Air Crisper and the Ninja Speedi using slow cook and both worked exactly the same, but I still encourage everyone to check on the ghee at least every 2 hours the first time you make it.