This is a simple blackberry jam recipe that includes shredded apples instead of commercial pectin. This recipe can be cut in half, if necessary.
Place a metal spoon in your freezer.
Wash blackberries and apples. Core apples, but do NOT peel.
Combine apples, blackberries and lemon juice in a large, heavy bottomed pot. Cook until soft.
Add sugar and stir to dissolve. Cook on medium-high heat until boiling, stirring constantly. Cook until mixture is reduced by at least a third, possibly a half. Don't forget to stir to prevent scorching!
After mixture has reduced, remove spoon from freezer and scoop a bit of jam onto it. Do "the spoon test" as per the instruction in the "Notes" section.
Bottle quickly into pint jars, remove air bubbles with a knife down the inside of the jar, wipe rims and place seals on top. Process in a water bath canner for ten minutes, adjusting for your altitude.
To conduct "the spoon test" to test for jam set, do the following.