Preheat oven to 375 degrees.
On a lightly floured surface, unfold the sheet of pastry and roll it into a 10 X 12” rectangle. Transfer to a parchment-lined baking sheet. Using the tip of a knife, score a 1-inch border around the pastry without cutting all the way through. Brush the border with egg and sprinkle with granulated sugar. Bake until golden and puffed, 18 to 22 minutes.
Using the tip of a knife, rescore the border of the cooked pastry without cutting all the way through. Gently press down the center of the pastry sheet to flatten it. Let cool to room temperature, 15 to 20 minutes.
Meanwhile, with an electric mixer, beat the cream cheese until smooth. Add the cream, lemon zest and 2 Tablespoons of the confectioners’ sugar. Beat until smooth. Spread the cream cheese mixture evenly within the border of the pastry. Arrange the blueberries in a single layer over the filling and sprinkle with the remaining Tablespoon of confectioners’ sugar. Cut and serve.