After rinsing, place the dewberries in a saucepan then toss with the sugar, lemon juice, and lemon zest. Allow to sit for 15 minutes or until softened and starting to release some juices.
Place a plate in the freezer. You will be using this later to test the doneness of the jam.
Turn the heat under the saucepan to medium high and smash the berries with a masher. While occasionally stirring, cook until the jam has thickened or has reached a temperature of 220°F, about 15-20 minutes. As it cooks, the jam will get foamy but that’s normal.
To test if the jam has set, place a spoonful of it on the plate that’s been in the freezer. After a few seconds if the jam doesn’t run it’s ready.
Pour into the jam into the prepared pint jar and refrigerate. It will keep for 1 month.
This recipe can easily be scaled up or down, though you will need to adjust the cooking time accordingly.