Step 1

Unwrap and add all of the butter to a large, heavy-bottomed stockpot. Place the stockpot over the lowest heat you can manage on your cooktop. If you have a low-powered simmer burner, it is ideal for this job. Melt down the butter and let it cook for 4-6 hours, stirring every so often, until there is a layer of deep, golden, clear, pure butter fat with toasted solids at the bottom of the pan and possibly some foam floating on top. Do not BOIL the butter! The low heat should keep it steadily percolating at an extremely low simmer, but not boiling.

Step 2

Line a fine-mesh sieve with a clean piece of muslin or flour-sack towel. If you don't have a fine-mesh sieve, you can line a colander with a double thickness of muslin or a flour-sack towel. Position this over a heat-proof pitcher or large bowl. Ladle the butter into the lined sieve or colander. When it has all strained, pour it into the jars to within 1/2-inch of the top. Wipe the rims, fix lids in place and let cool completely before labeling and storing.