Saw the frozen puffed pastry sheet in half. Puffed pastry comes folded in thirds. Gently pry apart each half neatly breaking the pastry into 6 pieces. Place the pastry on a lightly greased baking sheet and thaw approx 30 minutes. Bake in a preheated 400 degree oven for 15 minutes or until golden brown. Cool on a rack for a few minutes. Place each piece on a cake plate.
While the pastry is baking prepare the blueberry syrup. Place 1/2 cup of blueberries, sugar, cornstarch, water and lemon juice in a small saucepan. Bring to a boil then turn down the heat to a slow simmer stirring occasionally. When the sauce is the desired thickness stir in 1/2 cup blueberries and simmer 1 more minute. Remove from the heat.
Gently slice each pastry open with a serrated knife. Ladle a couple of tablespoons of the syrup onto the bottom half of each. The syrup should be nice and thick with cooked blueberries in it. Divide half of the remaining fresh blueberries among the pastries and close the top half over each. Ladle a couple of tablespoons of the syrup over each pastry.
Garnish with the remaining blueberries, dust with powdered sugar and serve.