Mix Dough– In a food processor combine the all purpose flour, whole wheat flour, sugar and salt. Add butter and process for another 5 seconds. Add egg yolks and 3/4 cup of cold water and process until dough is soft. Line a baking sheet with parchment paper.: The air is cool and the flour smells faintly of grain, and as you pulse all purpose flour , whole wheat flour , sugar , and salt with bits of cold butter you will hear small clumps collapsing into coarse crumbs, which is the right texture before adding liquid. This texture ensures that pockets of butter remain to create flakiness during baking. If you overprocess, the dough can become too uniform and lose its tender layers, so stop while you still see pea sized bits. A common mistake is warming the butter in your hands, which eliminates those flaky pockets, so work quickly and keep tools chilled.
Prep– Turn the dough onto a lightly floured surface and knead until smooth. Cover in plastic wrap and let rest for 30 minutes in fridge before using. Preheat oven to 400℉.: When the dough comes together and you knead it gently, you should feel it become smooth and elastic under your palms, not sticky. Wrapping it and resting it in the fridge firms the butter back up and relaxes gluten, which helps when rolling. Preheating the oven to 400℉ ensures a hot environment so the pastry sets quickly and flakes, rather than slowly absorbing filling juices. Avoid skipping the rest period, because warm dough will shrink and resist shaping, making sealing harder. If your kitchen is warm, chill the dough longer to keep the butter solid.
Mix Filling– In a bowl pour vanilla extract over blueberries and toss. Add flour and sugar over blueberries and toss.: Tossing blueberries with vanilla extract , all purpose flour , and sugar releases a sweet aroma as the juices start to coat the berries; the flour helps those juices turn slightly syrupy while baking. You want the berries coated but not crushed, so handle gently to preserve some whole fruit texture. This step prevents a runny filling that could wet the dough base. A typical error is adding too much flour which makes the filling pasty, so stick to the measured amount for balance.
Roll Out & Cut Dough– Roll out the empanada dough so that it's about 1/8 of an inch in thickness. Cut the dough into 4 inch rounds.: Rolling the dough to about one eighth of an inch gives a delicate shell that crisps without becoming brittle, and the surface should show slight specks of butter . Use a round cutter to make four inch circles, and work on a lightly floured surface to prevent sticking. Keep unused dough refrigerated as you work to avoid softening. Overworking the dough can make it tough, so roll gently and lift carefully; if it tears, patch with a little dough rather than overworking the patch area.
Make Empanadas– Spoon about 1 tbsp of goat cheese and a couple tbsp of prepared blueberries onto the center of each round, then fold dough in half enclosing the filling. Press the edges together to seal, then crimp either with your fingers or fork. Transfer empanadas to the prepared baking sheet.: When you spoon about one tablespoon of crumbled goat cheese and a couple tablespoons of the prepared blueberries into each round, you will notice the contrast of creamy and juicy textures, and that is the heart of the flavor. Fold and seal, crimping edges to trap steam and juices inside, which helps the filling become jammy without leaking. If you overfill, the pastry may burst and juices will escape, so keep portions modest. A frequent misstep is sealing with dry edges, which prevents a snug seal; moisten the rim lightly with water or egg wash if needed.
Bake & Serve– Brush each empanada with egg wash and using a fork poke holes into each empanada. Sprinkle top of empanadas with turbinado sugar. Bake for 15 to 18 minutes or until golden brown. Serve.: Brushing each empanada with an egg wash gives a glossy, golden crust and sprinkling turbinado sugar yields a delightful sparkle and crunch as it caramelizes. As they bake for 15 to 18 minutes, you should hear the quiet tick of cooling pans and see the crust turn a warm golden hue, with sweet steam scenting the air. Bake until the pastry is set and the bottoms are not soggy, rotating the sheet if your oven has hot spots. Avoid opening the oven repeatedly, which drops temperature and can result in underbaked centers. When done, let them rest briefly so the filling sets, then serve warm or at room temperature.