WONDERFUL SUGGESTION FROM A READER! Thanks for this... let us know how it works!
1. Use any butter that is on sale. Lesser quality butter requires more shaking (see #5 below), but the results are the same as with the expensive brands.
2. Heat pint jars in a 250 degree oven for 20 minutes, without rings or seals. One pound of butter slightly more than fills one pint jar, so if you melt 11 pounds of butter, heat 12 pint jars. A roasting pan works well for holding the pint jars while in the oven.
3. While the jars are heating, melt butter slowly until it comes to a slow boil. Using a large spatula, stir the bottom of the pot often to keep the butter from scorching. Reduce heat and simmer for 5 minutes at least: a good simmer time will lessen the amount of shaking required (see #5 below). Place the lids in a small pot and bring to a boil, leaving the lids in simmering water until needed.
4. Stiring the melted butter from the bottom to the top with a soup ladle or small pot with a handle, pour the melted butter carefully into heated jars through a canning jar funnel. Leave 3/4" of head space in the jar, which allows room for the shaking process.
5. Carefully wipe off the top of the jars, then get a hot lid from the simmering water, add the lid and ring and tighten securely. Lids will seal as they cool. Once a few lids "ping," shake while the jars are still warm, but cool enough to handle easily, because the butter will separate and become foamy on top and white on the bottom. In a few minutes, shake again, and repeat until the butter retains the same consistency throughout the jar.
6. At this point, while still slightly warm, put the jars into a refrigerator. While cooling and hardening, shake again, and the melted butter will then look like butter and become firm. This final shaking is very important! Check every 5 minutes and give the jars a little shake until they are hardened in the jar! Leave in the refrigerator for an hour.
7. Canned butter should store for 3 years or longer on a cool, dark shelf. [It does last a long time. We have just used up the last of the butter we canned in 1999, and it was fine after 5 years.] Canned butter does not "melt" again when opened, so it does not need to be refrigerated upon opening, provided it is used within a reasonable length of time.
I buy butter on sale, then keep it frozen until I have enough for canning 2 or 3 batches of a dozen jars each.