01 -
In a medium bowl, combine chopped rhubarb, sugar, cornstarch, vanilla extract, lemon juice, and ground cinnamon. Stir until the rhubarb is evenly coated and set aside.
02 -
Preheat oven to 400°F (200°C). Line a baking sheet with parchment paper. Unfold thawed puff pastry sheets and cut each sheet into 4 equal rectangles.
03 -
Spoon rhubarb mixture onto the center of half the pastry rectangles, leaving a 1/2-inch border. Top with remaining rectangles and press edges to seal with a fork.
04 -
In a small bowl, whisk together the beaten egg and milk. Brush the tops of the sealed pastry pockets with the egg wash for a golden finish.
05 -
Transfer pockets to the prepared baking sheet and bake for 20–25 minutes, or until puffed and deeply golden brown. Let cool slightly before serving.