Preheat the oven to 180c. 

In a small bowl, stir together one heaping cup of blueberries*, 3 tbs sugar, 2 tbsp cornstarch, 1 tsp lemon juice, ¼ tsp cinnamon, and a pinch of salt. Set aside.

On a lightly floured surface, roll out 250g puff pastry (it should still be cold) into a 26cm square.  Cut into four quarters and place each piece on a parchment-lined sheet.

Divide the blueberry mixture between the pieces and fold over the edges of the pastry (I like to just pinch the corners and fold it all in, but you can also fold in the edges in straight lines to make a frame). Brush the pastry with some beaten egg and sprinkle with sugar.

Bake for 20 minutes, or until bubbly and golden. Serve warm with cream or ice cream.

Note: You can pop these into the freezer, unbaked until ready to use. If baking from frozen they may need a few more minutes in the oven.

* If using frozen blueberries, use straight from the freezer.