Peel, core, and quarter pears. Put through grinder or process in food processor until it has the consistancy of applesauce. You should have about 2 quarts of pureed pears.
Cook all ingredients in crockpot for 8-12 hours. Set the crockpot on low heat. Cook time depends on the size and power of your crockpot, and how thick you like it, I let mine go overnight. It will reduce in volume by about half overnight.
About the last hour, use a wooden spoon or whatever you have handy to prop it open, because you want the steam to escape so it can thicken. Or use a large pot splatter-guard since it will spatter as it boils slowly.Wash the jars in hot, soapy water and rinse, then sterilize the jars by boiling them 10 minutes, and keep the jars in hot water until they are used. Keeping them hot will prevent the jars from breaking when you fill them with the hot pear butter.
Put the lids into a pan of hot, but not quite boiling water for 5 minutes. Fill jars to within 1/4 inch of the top, wipe any spilled pear butter of the top, seal the lid and tighten the ring around them.
Put them in the canner and keep them covered with at least 1 inch of water and boiling. Boil pint jars for 15 minutes, quarts for 20 minutes. If you use a pressure cooker, process for 15 minutes at 15 pounds.
Regarding the sugar quantities - It is best to use the lesser quantity, and taste the sauce as it nears completion. If it is not sweet enough, add additional sugar until it suits your taste. Keep in mind, however, that the pear butter will become sweeter as the liquid evaporates.