Whisk together the flours, salt, baking powder, and cinnamon in a large bowl. Add the butter and, using your hands, work it into the flour, making a crumbly mixture. Most of the butter should be in large, pea-sized pieces.

Stir in the Greek yogurt; the dough will be shaggy. Turn it out onto a lightly floured work surface, and bring it together with a few quick, gentle kneads.

Pat the dough into an 8" log, then roll it into an 8" x 12" rectangle. Dust both sides of the dough generously with flour, and starting with a shorter end, fold it in three, like a business letter.

Flip the dough over and roll it again into an 8" x 12" rectangle. Fold it in three again.

Wrap the dough in saran wrap; chill for at least one hour before using.

Peel and core apples. Dice them into tiny pieces and set aside.

Melt the butter in a large skillet over medium heat. Allow the butter to brown into a light golden color; about 1 minute. Add apples into hot butter; sprinkle with salt and both sugars. Cook, stirring occasionally, until apples are completely softened, about 8 minutes. Mix in cinnamon and bourbon; continue cooking until apples are soft and sticky, 1 to 2 more minutes. Stir in cornstarch, mix well, and allow mixture to thicken; about 2 minutes. Remove from heat.

When you're ready to make your pies, preheat the oven to 425 degrees (F). Line a large baking sheet with parchment paper; set aside.

Roll the dough out into a 14" x 14" square. Using a straight edge or pastry wheel, cut out sixteen 4" squares.

Divide the apple filling among 8 of the squares, using about 2 tablespoons for each. Brush some of the beaten egg along the edges of each filled square.

Cut a vent into the each of the remaining eight squares, using a decorative cutter of your choice.

Top each filled square with a vented square, and press along the edges with the tines of a fork to seal.

Brush the top of each pie with the remaining beaten egg, and sprinkle with sugar. Transfer the pies to the prepared baking sheet.

Bake the pies for 18 to 20 minutes. Remove them from the oven, and let cool for 20 minutes before serving.