Preheat oven to 400°F.
On a parchment lined baking sheet, roll out the puff pastry dough to a large rectangle.
In a small bowl, whisk together the egg and the water.
Use a knife to scour a border, 3/4 of an inch inside from the edge of the puff pastry.
Use a fork to pierce the inside of the tart several times.
Brush the pastry with the egg wash along the border.
Sprinkle with sparkling sugar if desired.
Bake for 20 minutes until golden brown and cooked. Set aside to cool.
While the puff pastry is cooking, prepare the topping.
In a large bowl, stir together the whipped cream, 1/2 cup white sugar, and mascarpone cheese.
In a separate bowl, mix together the strawberry slices, 1/4 cup white sugar, and strawberry jam.
Once puff pastry is cooled, top with the cream and then the strawberries.
Keep refrigerated until ready to slice and serve.
