Peel and slice pears very thinly. Place in a large bowl. Add sugar, ginger, and lemon slices; toss well to coat. Let stand overnight. In a large pot over low heat, cook, stirring often, about 3 hours. 

To test your jam to see if it’s done, dip a cold metal spoon into the boiling jam. Over a plate, turn the spoon on its side so the liquid runs off the side. The jam is done when it forms two drops that flow together and sheet or hang off the edge of the spoon.

Prepare boiling water canner and heat jars in simmering water until ready to use. Wash lids in warm soapy water and set aside.

Remove jam from heat and skim off any foam. Ladle hot jam into hot jars leaving a ¼ inch of headspace. Clean rims of jars before putting on jar lids. Screw the metal bands on finger tight and place in boiling-water bath canner. Process for 10 minutes.

Turn off heat and take off lid. After 10 minutes, remove jars and place on a rack or kitchen towel on the counter.  Allow jars of jams to cool down without moving. You may hear pinging…the jars have sealed!

After 24 hours remove the screw bands and test seal by pressing gently on the lid. If there is any give, it has not processed correctly and may be reprocessed or refrigerated for immediately use.

Store processed jam for up to a year in a cool, dry place.