Place the puff pastry round on the parchment lined baking sheet. Prick the pastry all over with a fork. Brush with the beaten egg and fold over about a ½ inch of the edge all around the pastry to form a border. Brush the edge with egg and then sprinkle sugar all over the pastry. Bake in the oven until completely cooked through and golden, about 10-15 minutes. (Don’t worry if you see some bubbles in your pastry, you can push these down later). Remove the pastry from the oven and allow to cool completely.
In a large bowl, whip the cream to soft peaks. Add the mascarpone, confectioner’s sugar, and the seeds of the vanilla bean. Continue to whip until well combined.
Press any bubbles that have formed on the surface of your cooled pastry down and spread the mascarpone cream mixture all over the top, leaving the border exposed. Top with raspberries and serve. The tart is best eaten the day it is made.