In a food processor, combine the flour, baking powder, and salt. Pulse until mixed, then add cold unsalted butter, cutting it until resembling coarse crumbs. Add sour cream and pulse until small clumps form.

Transfer the dough onto a floured surface and gather into a rectangle. Wrap tightly in plastic wrap and chill in the refrigerator for 10-15 minutes.

After chilling, roll the dough into a large rectangle. Fold into thirds, rotate 90 degrees, and repeat folding two more times. Wrap and refrigerate for at least 1 hour.

In a skillet, melt unsalted butter and sauté diced apples over medium heat until tender, about 5-7 minutes. Stir in brown sugar, golden sugar, cornstarch, and spices. Cook until thickened and cool completely.

Roll out half of the chilled dough and cut out circles, about 4-5 inches in diameter. Gather scraps and re-roll. Repeat with the second half.

On half of the dough circles, place 1-2 tablespoons of cooled apple filling. Cover with another dough circle and seal edges with a fork. Refrigerate assembled pies for 30 minutes.

Preheat oven to 425°F. Line a baking sheet with parchment paper and arrange the chilled hand pies. Cut slits in the tops for steam release, brush with egg wash, and sprinkle with sugar. Bake for 10 minutes, then reduce temperature to 365°F for an additional 15 minutes.