Heat oven to 375°F.
Unwrap one layer of puff pastry and place on a piece of parchment paper that is on a baking sheet. Trim off corners (if you want).
In a bowl, add sugar and cornstarch and sift together with a fork or whisk. Add in the blueberries and lemon juice and stir to coat.
Pour blueberry mixture into the center of the puff pastry. Start folding the edges up and over the edge of the fruit. Do this around entire puff pastry.
Crack an egg and beat it with a fork. Brush the puff pastry with the egg, covering it all.
Sprinkle with the raw sugar.
Bake for 15-25 minutes or until the pastry is a golden brown, not burnt.
When done, remove from oven. and let the pastry sit for at least 10 minutes, allowing the sweet fruit juices to thicken slightly.
Shave white chocolate over the top and serve. (If you want the white chocolate to be melted, add this right out of the oven.)