Preheat oven to 210 C . Place berries, apple and sugar into a medium saucepan and cook over medium-high heat, until berries have begun to release their juices.
Add almond meal and continue to cook the berries until sauce has thickened. Remove and let cool.
Place thawed puff pastry on a sheet of parchment paper .Cut sheet into 4 squares .
Place a large spoonful of the cooled filling into the lower corner of one puff pastry square brush the edges with water. Fold the opposite corner over into a triangle to seal. Use the tines of a fork to crimp the edges together.
Brush each turnover with milk and sprinkle slivered almonds. Bake for 15 to 20 minutes, until golden brown. Check halfway through baking and turn the pan around if one side is browning faster than the other. Serve warm...