1.In a food processor with the blade attachment, pulse 1 1/4 cups flour, sugar and salt until well mixed.
2.Cut 1/2 cup cold butter into small cubes and add it to the food processor. Push the pulse button 8 times. Your butter should become pea-sized. Add ice water 1 Tbsp at a time and pulse between each addition. Your dough should be ready when it just begins to clump.
3.Form the dough into a disk. Don’t overwork it, just pat it into a disk shape, dust with flour on all sides and cover with plastic wrap. Refrigerate for 1 hour.
4.Preheat the oven to 425°F. Take out a sheet pan and cover with parchment paper. In a small bowl, beat the egg and set aside.
5.Place peaches in a medium bowl and sprinkle with flour, brown sugar, cinnamon, nutmeg, bourbon, and vanilla. Stir gently with a spatula just until combined. Set aside.
6.Roll the dough into a 12″ circle. Place the dough into the prepared sheet pan. Arrange the peaches in circles over the dough working from the outside in. Leave a 2″ dough border. Discard any excess juices from the peaches. Dot the top of the peaches with small chunks of 1/2 tbsp butter.
7.Fold the edges of the gallette up and over the peaches, pinching the overlapping edges together to form a nice seal. Brush the crust with beaten egg and sprinkle with cinnamon and turbinado sugar. Bake for 18-22 minutes until the crust is golden brown and the peach juices are syrupy.
8.Meanwhile, add whipping cream and 1/4 teaspoon of vanilla extract to the bowl of a stand mixer. Whip on high for a minute then add powdered sugar. Whip on high again until you see medium peaks.
9.Take gallette out of the oven and let sit 15 minutes before serving. Top with whipped cream right before serving.