Cut out berries into pieces. Sprinkle with sugar, cinnamon and cornstarch. Mix together. Set aside for 5-10 minutes.
On a lightly floured work surface, roll out the dough 3-4 mm thick. Spread berry mixture into a circle in the center of the dough leaving border of dough uncovered along the edge.
Fold the edge of the dough up and over the berries, leaving the galette uncovered in the center.
Refrigerate the galette for 30 minutes.
Preheat the oven 365F. Sprinkle sugar on the edge of the galette. Bake 365F 35-40 minutes, until crust is brown.