Lemon Curd:

1. Preheat an oven to 350ºF and line a rimmed baking sheet with parchment paper.
2. In a small saucepan, heat the lemon juice, sugar, and butter together while whisking just until the butter melts. Have a heatproof bowl with a whisked egg in it ready.
3. Pour 1/2 of the stove mixture into the bowl with the egg and whisk vigorously until combined.
4. Pour the egg mixture back into the saucepan with the rest of the lemon juice and heat on low while whisking until it is thick and reaches 180ºF 
5. Pour into a bowl and cover with clingfilm directly onto the surface until cooled.

Blueberry Jam:

1. In a small saucepan (cleaned from lemon curd), heat blueberries, granulated sugar, water, and lemon zest for five minutes until thick and saucy.
2. Let cool

Turnover Assembly:

1. On a clean floured cutting board, roll out puff pastry between 1/8-1/4 inch.
2. Cut into 12 even squares with a sharp knife or pizza roller.
3. Spoon 1 scant tablespoon of lemon curd into the bottom left corner of each square leaving a 1/4 inch border. Then spoon 1 heaping teaspoon of blueberry jam to the right of the lemon curd.
4. Brush a small amount of water onto the border of each square and fold the empty side of the puff pastry square diagonally onto the other side.
5. Seal each turnover fully with a fork in a crimping fashion. Cut a small slit on the top of each turnover with a pairing knife or kitchen shears. Brush the tops of the pastry with egg wash.
6. Transfer each turnover onto the lined baking sheet and cover the top with a damp towel. Chill in the fridge for twenty minutes.
7. Once chilled, bake for 15-20 minutes until dark golden brown.