Place the flour on a work surface and make a well in the center. Cut the butter into small pieces and with a pastry blender, cut the butter into the flour until it resembles coarse crumbs. Add the egg and a little water and quickly knead until the dough comes together. Shape into a flat disk, wrap in foil and refrigerate 1 hour.
Set custard cups upside down on the work surface and place a round of parchment paper on the bottoms. On a lightly floured work surface, roll the dough out to 1/8-inch thickness and cut out circles larger than the custard cups. Drape the circles of dough over the paper, pressing the dough around the custard cups. Place upside down on a baking sheet.
Preheat the oven to 200°C (approximately 390°F). Bake 20 minutes, cool on a wire rack and remove the bowls and paper.
Rinse the fruits, pat dry and toss in a bowl with the sugar and marinate briefly. Fill the pastry shells with the berries and garnish with mint.