Put the blackberries in a small saucepan, mash a bit with a fork or potato masher, and simmer over medium-low heat for 10 minutes. That's it! Refrigerate for later use. It will firm up if left overnight in the fridge.
Assemble the Parfait
Add about half of the yogurt into a small bowl and mix a spoonful of jam into it, mostly just for the pretty color.
Layer the pretty yogurt, jam, regular yogurt, granola, and berries in a glass jar or cup.
Admire, and enjoy!
I like to make a big batch of blackberry jam at a time, but because there are no sugar or preservatives added, it should not be canned using traditional methods. It does freeze well though! I usually make more than I can eat and freeze it in small jars with about 1/2 inch of room left at the top to allow for expansion.