In a medium saucepan, whisk together the lemon juice, lemon zest, granulated sugar, and milk or heavy cream over medium heat. Cook until thickened and bubbling, about 5-7 minutes. Remove from heat and cool in refrigerator for at least 1 hour.

Preheat oven to 400°F (200°C). Roll out puff pastry sheets on a floured surface, cut into squares or circles, and arrange on parchment-lined baking sheets. Brush with heavy cream and sprinkle with sugar.

Bake for about 25 minutes until puffed and golden brown. Remove from oven and cool on a wire rack.

While shells are warm, hollow out the centers using a spoon to create a well for the lemon cream. Cool completely.

Transfer cooled lemon pastry cream into a piping bag and fill each pastry shell generously.

Top each pastry with fresh blueberries and dust with powdered sugar just before serving.