Preheat your oven to 375°F.
In a bowl, mix together the sliced strawberries, sugar, melted butter, and vanilla extract.
Pour the strawberry mixture into a 9-inch tart pan.
Roll out the puff pastry sheet and place it over the strawberry mixture, tucking in the edges around the sides.
Brush the top of the puff pastry with the beaten egg.
Use a sharp knife to make a few small slits in the top of the puff pastry to allow steam to escape.
Bake the tart for 35-40 minutes, or until the pastry is golden brown.
Remove the tart from the oven and let it cool for 5-10 minutes.
Carefully flip the tart over onto a serving platter, so that the strawberries are on top.
Serve the tart warm or at room temperature, topped with whipped cream or vanilla ice cream, if desired.