Preheat the oven to 200 degrees Celsius/ 400 degrees Fahrenheit. Line a large baking tray with baking paper.
Turnovers
Unroll the pastry on the working surface. Cut into squares; I had 18 small ones. Bake for about 15-20 minutes or until deeply golden and puffed.
Fill: Spread about ½ teaspoon Nutella on half of the squares, leaving enough space for the edges to be crimped shut. Place 1 small strawberry or ½ a large strawberry in the middle.
Form turnovers: Cover with the remaining squares. Using a fork, press the edges of the turnovers with the tines of the fork to seal the edges together. Using a small knife, make two small slits in the pastries (each side of the strawberry). Transfer to the prepared baking tray.
Egg wash: Whisk together the egg and the milk in a small bowl. Brush the turnovers with the mixture.
Bake for about 15-20 minutes or until deeply golden and puffed.
Glaze
Mix the icing sugar with enough lemon juice to obtain a smooth, thick, and slightly runny consistency. Start with 1 ½ tablespoon juice, add the rest drop by drop, stir in between, and check the consistency before adding more.
Glaze: Once the turnovers are baked, drizzle them with the glaze over the top using a spoon.
Let cool: Leave the pastries to cool for about 5 minutes, then carefully transfer to a wire rack to cool completely.
Notes
The recipe can be easily doubled.
Refrigerated ready-rolled puff pastry weighing 375 g/ 13 oz and about 48x26 cm/ 19x26 inches large, a little more or less is OK. The size of the pastry is not essential. Cut the dough into squares of about 8 cm/ 3-inches and make as many pastries as possible with the dough amount. You will need 1 small or ½ a large strawberry and about ½ teaspoon Nutella (if using) for each turnover.
You can use frozen pastry instead. Thaw and roll (if necessary) according to the packet instructions.
Small strawberries should be left whole; large ones should be halved.
Use as much as required to achieve a thick, slightly runny consistency. You can replace the lemon juice with milk or water.