Rinse the fresh blackberries under cool water using a colander. Be gentle to avoid damaging the fragile blackberries.
Lay the blackberries out to dry on a clean kitchen towel. Allow drying for at least 5-10 minutes.
Transfer dry blackberries to a parchment-lined cookie sheet, taking care to spread berries out evenly over the surface.
Place the baking sheet in the freezer taking care to keep it level. Allow to freeze for at least 3 hours, but no more than 12 hours.