In a bowl, combine dough ingredients together by hand. Knead until a dough is formed. Place in the refrigerator for 30 minutes, or, if doubling, divide the dough in portions and freeze for a later use.
Preheat oven to 375°F.
Place the dough between two pieces of parchment paper and using a rolling pin, roll out dough into a 10 to 11-inch circle. You want the dough to be of equal thickness all around. Peel back the top piece of parchment paper. Discard. Transfer the rolled out dough onto a baking sheet.
Combine all the filling ingredients in a bowl and mix well, so that the sugar and cornstarch are evenly distributed.
Pour the fruit in the center of the rolled out dough, leaving a 2-inch border. You can use your hands to spread out the fruit and kind of cluster it with some height onto the center. Using the parchment paper to help you, fold up the edges of the dough over the fruit and pinch into pleats.
Spray the crust with nonstick cooking spray (to help the sugar stick) and sprinkle generously with turbinado sugar. At this point you can freeze it as-is. When ready to bake, just defrost for about 20 minutes and bake.
Bake for 45-50 minutes, or until the fruit is oozing and the crust golden. If you see the fruit starting to burn, cover the pie loosely with a piece of foil.
Remove from oven and let cool for 15 minutes or so before cutting into the galette.