Allow puff pastry to thaw if frozen and place on a baking sheet lined with parchment.
Toss nectarine slices in a bowl with ginger and brown sugar. Arrange slices on top of puff pastry, leaving about a 1 1/2 inch edge. Fold edges in around the fruit to form a square.
If desired, dot fruit with butter and brush edges of pastry with egg wash (whisk together egg and milk).
Bake for 25-30 minutes, until pastry is golden and fruit is bubbly.
Enjoy with whipped cream or vanilla ice cream while warm.