In a saucepan over medium heat, combine blueberries, sugar, lemon zest, and juice, stirring well and mashing about ¼ of the berries. Cook rapidly for about 30 minutes or until the jam thickens. Stir frequently to prevent sticking.

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

Ladle hot jam into hot, sterile 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. Store for up to one year in a cool dry place.