Roll out the galette dough onto a lightly floured surface to a 13-15 inch circle. Place the dough onto a silicone baking mat or two pieces of parchment paper.
Sprinkle center of the dough with the coconut flour.
Arrange the cherries and peaches onto the dough in an even layer, leaving a 2 inch border of dough bare.
Next, fold the edges of the dough inward slightly overlapping the fruit. Create folds or pleats as you work your way around the galette. This will create an open center with a “pizza crust” look. Use cold water in the creases to seal the dough seams with your fingertips.
Stir the egg and water in a small bowl with a fork to create an egg wash. Use a soft pastry brush to lightly coat the folds of the dough. You can also use milk or cream if you prefer. then sprinkle with coarse sugar.
Transfer the galette to the fridge to allow the dough to chill for 20 minutes before baking.
Preheat the oven to 375 F (190 C), then transfer the galette still on the baking mat or parchment paper onto a large baking sheet.
Bake on the center rack for 30-35 minutes until the crust is golden brown and the fruit juices are bubbling.
Remove galette from the oven and place pan on wire rack for 5 minutes.
Transfer galette by sliding parchment paper off the cookie sheet and directly onto the wire cooling rack to prevent further cooking the bottom crust.
Slice and serve galette warm with ice cream.
Cool completely before storing.