• Thaw the puff pastry for 40 minutes at room temperature.
• Preheat the oven to 400℉ and line a baking sheet with parchment paper.

Make the filling

• While the puff pastry is thawing, make the filling on the stove.
• Make the filling by combining the blackberries, granulated sugar, lemon juice, and cornstarch on the stove and cook on medium for about 5 minutes, or until the juices start to come out of the blackberries and the cornstarch helps thicken any of the juices that come out.

Cut the puff pastry and assemble the turnovers

• Roll out your puff pastry to 10 inches by 14 inches and then cut it down the middle (the long way) and then make two cuts across, equally spaced, giving you 6 square pieces.
• Add about 1 to 2 tablespoons of the filling to the middle of each puff pastry piece, fold in half to form a triangle and press the edges together. Wipe away any excess juices that spill out.
• Make 3 small slits in each pastry, brush with the melted butter and add the raw sugar on top. Be careful to only add the raw sugar to the top of the turnovers, any that land on the parchment paper may burn.

Bake

• Bake for 15 minutes. Let cool on the baking sheet for about 10 minutes before transferring to a wire rack.

Add the icing

• If making the icing, stir together the heavy cream, powdered sugar, and lemon extract until smooth.
• Allow the turnovers to cool and then drizzle with the icing (if using) before serving.