In a small bowl, dissolve the sugar and salt in the water. Refrigerate until very cold, about 30 minutes. During that time, refrigerate your butter, flour, mixer bowl, and paddle, too.Make sure your butter is cut into 1/2-inch dice. Bigger pieces will make your dough puffy. In the chilled bowl, combine the cold butter and flour. With your hands, toss the butter in the flour until each cube is lightly coated.With the chilled paddle, beat the flour-butter mixture on low speed to just break up the butter, about 30 seconds. Add the water mixture all at once and raise the speed to medium-low. Beat just until the dough comes together in big chunks, then immediately turn off the mixer.Divide the chunks of dough in half and very gently pat each group into a round 1-inch-thick disk. Wrap each tightly in plastic wrap and refrigerate until firm, about 1 hour, before rolling.
Filling
Preheat oven to 400°F.Allow dough to come to room temperature while you prepare filling.In a large bowl, gently toss together Blueberries, Sugars, Salt, Vanilla, Cornstarch and Orange Juice and Zest.Roll out dough to 1/4 inch thickness. Place dough onto a cookie sheet with parchment underneath. Pour the Blueberry mixture into the center of the dough leaving a 2-inch border. Pleat the dough every 2-3 inches until you have created a rustic wall to hold the Blueberries.In a small bowl, whisk together one Egg and a splash of Water. Brush the exposed dough with the Egg wash. Sprinkle the dough with Turbinado Sugar. Bake for 40 minutes until bubbly and golden brown. Allow to cool for 10 minutes. Serve warm or at room temperature.
