These golden, flaky blueberry turnovers are filled with jammy homemade blueberry pie filling, wrapped in buttery puff pastry, and finished with a deep purple blueberry glaze made from the filling's leftover juice.
Cook the fresh blueberries with the water, sugar, and lemon juice over medium heat for about 8-9 minutes, or until the mixture bubbles and thickens slightly.
In a separate bowl, mix the cornstarch with water until smooth. Add a tablespoon of the warm blueberry sauce to the cornstarch mixture, then gradually pour the cornstarch mixture into the blueberry-sugar mixture. Stir constantly and cook for another minute until the blueberry pie filling thickens.
Set the blueberry filling aside and let it come to room temperature before using it.
Assembling
Line 2 sheet trays with parchment paper and whisk one egg with a dash of milk.
Roll out one thawed (if using frozen) puff pastry sheet on a lightly floured surface (or silicone baking mat) into a 15 x 30 cm / 6 x 12 inches rectangle. Cut it into 4 equal squares.
If the dough warms up and becomes difficult to handle, refrigerate it for 10 minutes; otherwise, continue with a light egg wash on the edges of each square.
Then, place about two tablespoons of filling in the center. Pay attention not to touch the edge with the filling. Leave about ½ inch (1 cm) around the border.
Fold one corner of the puff pastry over the filling to the opposite corner to form a triangle. Press your finger around the edges to properly seal them, then crimp with a fork.
If the pastry is still nice and cold, apply a light egg wash.
Using a toothpick or knife, poke three small holes on the top of the pastry. Be careful not to dig deep into the bottom of the pastry.
Place the unbaked turnovers in the freezer for 10 minutes while preheating the oven to 200°C / 390°F.
Bake the blueberry turnovers at 200°C / 390°F for about 25 minutes, or until the top is golden brown and the bottom is evenly baked. If the pastry browns too much, cover it with aluminum foil.
Let them slightly cool in the baking tray for 5 minutes then move them onto a cooling rack.
Dust with powdered sugar and serve them fresh. Or try a simple decoration: mix powdered sugar with 1-2 tablespoons of blueberry juice and drizzle it over the turnovers.
Store leftovers in an airtight container at room temperature for up to a day, or wrap them in plastic wrap and refrigerate for up to two days.
Notes
Ingredient notes
Use all-butter puff pastry for the best flavor and texture.
If possible, use fresh blueberries. Frozen blueberries release too much water, need to cook longer, may need more cornstarch, and lose their shape by the time the mixture thickens.
For noticeably better layers and a richer result, use homemade rough puff pastry instead of store-bought.
If you have no blueberry juice for the glaze, substitute it with milk.
Technique notes
Work as quickly with the pastry as you can, as over time, when the pastry warms, it will stick, which makes it very difficult to handle.
The blueberry filling must be completely cold before assembling. Warm filling would melt the dough.
Check the bottom of the pastry - whether it is well baked - before removing the pastries from the oven.