Place black raspberries, sugar and lemon juice into a medium sized saucepan. Make sure there's plenty of room in the pan to prevent it from bubbling over- the liquid will get quite bubbly.
Cook the raspberries on medium heat until they have released their juices. Use a spoon to crush the raspberries against the pan as you stir.
Once the berries have released their juices, turn the heat up to high and boil rapidly.
Thicken the jam by continuing to boil for around 8-10 minutes or until your jam reaches gel stage (see notes below).
Once the jam reaches gel stage, remove from heat immediately and fill jam jars leaving 1/4 inch headspace.
If using immediatly, you can store in the refrigerator , or if canning, process in a water bath canner for 5 minutes. After 5 minutes, turn off the heat and leave the jars in the water for an additional 5 minutes before removing to help prevent liquid in the jar being forced out by improper cool-down procedure.
Allow the jars to cool completely. Check that jars have sealed properly and store for up to a year.