Center a rack and preheat oven to 425℉ Line a baking sheet with parchment paper and set aside
Peel and slice the peaches into a medium size bowl. Add the sugar, flour, cinnamon and vanilla. Gently stir to combine. Let it sit for about 10 minutes
Meanwhile, roll the pie dough out flat on the parchment lined baking sheet
Using a slotted spoon, lift the peach slices out of the bowl (leaving the juices in the bowl) and onto the center of the pie dough, mounding them in the middle leaving a band of about 2 inches bare all around.
Pick up the edges of the dough and fold them up against the peaches. As you fold, the dough will bend and pleat on itself-that's what you want it to do. You don't have to be precise. Remember, this is 'rustic'! Scatter the pieces of butter on the peaches.
If there is a crack in the dough, fix it by smoothing it with a little water on your finger, pressing it together.
Make an egg wash by whisking the egg in a small bowl and add about 1 tablespoon water to thin it down. Brush the folded edges of the dough with the egg wash then sprinkle it with the turbinado sugar.
Bake the galette for 30 minutes, or until the crust is brown. Remove from the oven and serve immediately. A scoop of vanilla ice cream is so delicious on top, but it wonderful all on it's own.