Prep your jars, as well as the lids and bands. Make sure everything is clean and dry.
Wash and rinse your berries, especially if they're fresh berries. Pat dry.
Purée or crush the berries, using a blender, potato masher, or food processor, for 2 to 3 minutes.
In a stock pot, mix together the crushed blackberries, sugar, and lemon juice.
Heat the mixture on low to medium heat, and bring it to a boil, stirring constantly with a spatula, so it doesn't scorch.
Boil the mixture for a good 20 to 24 minutes, stirring constantly. The sugar should all dissolve in the boiling process.
Remove the mixture from the heat, and let it set a few minutes.
If you have any foam on top, you'll want to skim that off; this may or may not be necessary.
Note: Your jam will seem more like syrup at this point. Please don't be discouraged, because it works a little bit like magic from here on.
Pour the mixture into a 9x13 cake pan, and let it stand until it cools, 3+ hours. As it cools, it will begin to set and jell. Before you know it, you'll have the thick consistency of jam; it feels like magic, but it's actually a combination of the natural pectin in the berries and the cooling process that does the work of thickening or setting the jam.
Canning Blackberry Jam:
Wash half-pint jars and lids in hot soapy water, rinse, and keep warm. We like to place ours on a baking sheet in a lower temp oven to stay hot.
Using a jar funnel, ladle or pour the jam into the hot jars. Be sure to leave about a 1/2-inch gap at the top of each jar.
Wipe the rim of each jar with a wet towel or rag, place the lid on, and tighten the band.
Then place the hot jars down in a boiling hot water bath canner with 1-2 inches of water over the jars, and process those jars in the hot water bath for about 10 minutes.
Remove the jars from the oven, and allow them to rest for at least 24 hours, but be sure to check every lid to make sure it's sealed shortly after canning.
Before moving to the pantry, remove the bands and write what it is and the year on the lid, so you know when you made it.
Freezing Blackberry Jam:
Using a jar funnel, ladle or pour the jam into the clean jars. Be sure to leave about a 1/2-inch gap at the top of each jar to allow for expansion in the freezer.
Wipe the top of each jar with a wet towel or rag, place the lid on, and tighten the band.
Before you put your jam in the freezer, be sure to write what it is and the year on the lid, so you know when you made it.
Serve the jam on toast, biscuits, ice cream, etc.
While fresh are better, you can use frozen blackberries. Just be sure to thaw them ahead of time, so they don't add unnecessary liquid to the mixture and they're easier to crush.