Preheat the oven to 425°F.
Flour your work surface and rolling pin slightly. Line a baking sheet with parchment paper. Roll out the dough with a rolling pin to a 12 inch square. You can trim the edges with a sharp knife or a pastry cutter. If the dough is beginning to warm up and get too soft, refrigerate or freeze it until it hardens up a little bit and easier to work with. Prepare the egg wash by mixing 1 egg and 1 tablespoon of milk with a fork.
Spread the frangipane evenly on the crust, leaving about 2-3 inches edge. Then arrange peaches on the frangipane, leaving the fruit juices behind.
Fold the edges and brush them with egg wash. Sprinkle some sliced almonds and granulated sugar on top if you'd like. Refrigerate it on the baking sheet for 20 minutes, or freeze it for 10 minutes.
Bake in the preheated oven for 35-40 minutes or until the filling is bubbling and the crust is golden. In the meantime, you can prepare the glaze.
The glaze is optional but it creates a beautiful shine on the galette. In a small pan, add in apricot preserve and water. Heat on medium heat and stir occasionally until the preserve melts and the mixture thickens a little bit. Set aside.
Let it cool down for 10 minutes. Then brush the peaches with the glaze. Serve warm or at room temperature with a dollop of whipped cream or a scoop of vanilla ice cream. Enjoy!