Thaw puff pastry sheet according to package instructions. Lay out thawed puff pastry on a parchment paper lined baking sheet.
In a large bowl combine sliced nectarines, blueberries, white sugar, flour, and vanilla. Stir to combine. Pour the fruit mixture out in the center of the crust, with a 2-inch border.
Fold in the edges of the dough, around the fruit filling.
Brush the edges of the pastry with a little milk and sprinkle the whole galette with some Demerara sugar.
Bake at 450 degrees for about 12 -15 minutes until golden brown.