Peel, core, and chop apples into ½-inch pieces (you should have 2½ cups).
In a medium saucepan, combine apples, 2 tbsp maple syrup, and ½ tsp apple pie spice. Cook, covered, over medium for 4–6 minutes until apples soften, stirring occasionally.
In a small bowl, whisk 1 tbsp cornstarch with 2 tbsp water until smooth. Add the slurry to the apple mixture and cook 1 minute while stirring, until thickened. Remove from heat and cover to keep warm.
Make the crust (flaky-ish whole wheat pastry)
In a small bowl, stir 1 tbsp flaxseed meal with ¼ cup water; let stand 5 minutes (this forms a flax “egg”).
In a food processor, combine 1½ cups whole wheat pastry flour, ½ cup quick oats, and ¾ tsp sea salt. Pulse until the oats grind coarsely.
Add 3 tbsp cashew butter, 1 tbsp sugar, and the flax mixture. Pulse until dough barely holds together. Add 3–4 tbsp water, 1 tbsp at a time, pulsing until the dough clumps.
Knead dough once or twice on a lightly floured surface to even it out. Wrap in plastic and let sit 20 minutes.
Assemble the hand pies
Preheat oven to 400°F (if baking) or preheat air-fryer to 375°F (air-fryer temps vary; see tips). Line a baking sheet with parchment.
Divide dough into 4 equal portions. Lightly dust one portion with flour, place between two sheets of parchment, and roll to a 10×5-inch rectangle (~1/8 inch thick). Remove the top parchment. Cut rectangle in half to make two 5-inch squares. Repeat for remaining dough.
Spoon ~3 tbsp of apple filling down one half of each square, leaving a ¼-inch border. Brush edges with 1 tbsp plant-based milk. Fold unfilled half over and press edges with a fork to seal. Cut a few slits on top to vent.
Place pies 1 inch apart on the prepared sheet.
Finish & bake / air-fry
Mix remaining 2 tsp sugar with ⅛ tsp apple pie spice. Lightly brush tops with milk and sprinkle sugar-spice.
Oven: Bake 20 minutes or until bottoms brown lightly. Tent with foil if tops brown too fast. Serve warm.
Air-fryer option: Arrange pies in a single layer (work in batches). Air-fry at 375°F for 10–12 minutes, checking at 8 minutes, until golden. Air-fryer models vary — adjust time slightly.