Mix the flour, cold butter, water, egg yolks, salt, and sugar together in a food processor or cut the butter into the dry ingredients and eggs with a pastry cutter in a bowl. When finished, the dough should be pea-sized and resemble wet sand.
Transfer the dough from the food processor or bowl to a lightly floured surface or a piece of parchment paper. Use your hands to shape the dough into a disk shape. Wrap the disk in plastic wrap and chill in the fridge for 45 minutes to 1 hour.
To make the filling, combine all ingredients in a medium bowl and toss gently. Once everything is coated well, set aside.
Remove the dough from the refrigerator and place on a sheet of parchment paper. Starting at the center of the dough, roll it out with a rolling pin into a 14-inch wide circle. Place the parchment paper with the dough on a baking sheet.
Add the filling to the center of the dough, leaving a 2-inch border. Fold the border over the filling, overlapping where necessary and pressing gently to adhere the folds.
Whisk one egg yolk in a bowl. Using a pastry brush, brush the crust of the galette edges with the egg yolk. Add turbinado sugar on top of the edges.
Bake for about 30-40 minutes or when the dough is golden brown and crisp.
Remove the galette from the oven and let it cool for about 10 minutes on a cooling rack before cutting. Serve with ice cream or whipped cream, optional.