Peel and de-seed butternut squash. The rind is quite hard, so you may not be able to peel it with a vegetable peeler. I find it easiest to peel long strips along the neck of the squash. Then, but the squash in half, and scoop out the seed cavity.
Cube the squash into about 1 inch cubes
Pack squash loosely into sterilized jars
Stop pint jars with 1/2 teaspoon salt, or quart jars with 1 teaspoon of salt
Cover squash with water, leaving about an inch of headspace
Screw lids and rings down firmly
Place in prepared canner (you canner should have come with instructions. Typically isn’t something like adding the inner rack and adding 2 quarts of water to the bottom
Secure lid onto canner, with steam valve open. On a weighted gauge canner, this usually just means removing the weight gauge
Heat canner over medium-high heat until a steady stream of steam escapes the valve, and let connate to steam for 10 minutes
Close valve, and bring canner to 10 pounds of pressure at sea level (for those at elevations, use this conversion chart)
Once pressure level is reached, process pint jars for 75 minutes, and quart jars for 90 minutes
Remove canner from heat, and let return to zero pressure naturally
If needed, at this point you can open the valve to ensure all pressure is released, open the lid, and carefully remove jars, protecting them from drafts with a towel. Set the jars in a place where they can remain undisturbed while they cool, and cover with another towel.
After 24 hours, check for seal, wash hardware stains, or stickiness off if needed, and store in a cool place out of direct light.