In a food processor with the blade attachment, pulse together the flour, sugar, and salt until combined.

Cut cold butter into small (½-inch) cubes and add it to the food processor. Push the pulse button 8-10 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.

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 at least 1 hour or up to 3 days.

Preheat the oven to 425°F. On a floured sheet of parchment paper, roll the dough into a 12″ circle with a rolling pin. It doesn't have to be a perfect circle. Place the parchment paper and dough into a rimmed baking sheet and refrigerate while you make the peach filling.

In a small bowl, stir together granulated sugar, flour and cinnamon. Slice peaches into ½″ thick slices, place peaches in a medium bowl and sprinkle with flour mixture. Add vanilla and stir gently with a spatula until the flour is fully incorporated.

Arrange the peaches in a circular pattern over the dough working from the outside in and leaving a 2″ dough border. Discard any excess juices from the peaches, or your galette may overflow. Dot the top of the peaches with small chunks of ½ tbsp butter.

Fold the edges of the galette up and over the peaches, pinching the overlapping edges together to form a nice seal. Try to patch up any cracks in the dough. Brush the crust with beaten egg and sprinkle with coarse sugar. Bake for 25-30 minutes until the crust is golden brown and the peach juices are syrupy. It's ok if it juices start oozing from the bottom. Let sit 15 minutes before serving.