Sort and rinse fresh blackberries. Puree the berries and 1 tablespoon of powdered sugar with the blender. Strain the berry puree through a sieve. Beat the egg and the remaining powdered sugar with the whisk of the hand mixer until light yellow and creamy. Gradually stir in the berry puree and yoghurt. Pour the mixture into the ice cream molds, close the molds and let the ice cream freeze in the freezer for at least 6 hours.