Defrost the blueberries if frozen. Dry them with a cloth or paper towel and cut them in half. If using fresh blueberries simply cut them half.
Toss the blueberries in a large bowl with sweetener of choice and oil. Spread out as thinly as you can on a large baking tray lined with baking paper.
Bake for 3-4 hours until the blueberries have dried out sufficiently. Check them at 3 hours to ensure they aren't drying out too much and then keep a regular eye on them until they have dried out enough.
If they have dried out enough they can be stored in an airtight jar in the fridge. If they still have a little moisture in them they are more susceptible to going off, so store them in the freezer.
The yield from this recipe is approximately 130 gms/4.5 oz of dried blueberries.
Adjust the sweetener to your taste. My preference is for a slightly tart lightly sweetened blueberry and the recipe reflects this.A dehydrator can also be used to dry blueberries in lieu of the oven method.