Place a couple of small plates in the freezer.
If using fresh raspberries, wash and pick out any stems or leaves.
Place fresh or frozen raspberries, sugar, and lemon zest and juice into a pot large enough that the berries comes halfway up the side of the pan.
Cook on medium heat until mixture begins to simmer, continue cooking for 10-15 minutes until the jam reaches 220° F. You can also check the jam by place a small spoonful on the cold plate, let it sit for a few seconds and then try to push the jam with your finger. It should wrinkle, if it’s still liquid when you push, your jam needs more time. Put the plate back into the freezer and keep cooking the jam, checking every few minutes using the plate test to see if the jam has set.
Pour into jars and cover loosely with the lids. Let cool for about an hour. Tighten lids before moving them into the fridge.