Add a pot over a medium heat, stir regularly until the berries begin to release their juices.
Gradually add sugar, 1/2 cup at a time.
Add lemon juice
Stir continually using the back of your spoon to mash large bits of berries.
Continue to stir while jam simmers allowing it to thicken slightly, about 20-30 minutes
The jam will be runny because it’s hot, but you can test for doneness By dipping a metal spoon into your jam. Your jam is ready when the spoon is coated with a visible layer of jam that doesn’t drip off easily.
Notes
If you find your jam isn't setting properly, try adding 1/2 cup of sugar and continuing to cook.