In a medium-sized bowl, stir together the walnuts, melted butter, brown sugar, ½ teaspoon cinnamon, nutmeg, and cardamom until well combined.
Add the apple slices to the brown sugar mixture and stir until the apples are thoroughly coated.
Unwrap the pie crust and spread it out on a cutting board or work surface. With a knife or pizza cutter, trim the edges to create a rectangle that’s roughly 10 inches x 8 inches. Cut the dough into 8 even strips (10 inches long x 1 inch wide).
Place an apple slice at the end of each strip. Then starting the end with the apple slice, roll up the pie crust strip around the apple until it's wrapped up like a mummy. Pinch the end of the dough strip to the dough wrapped around the apple to seal it.
Brush the milk onto the top of each apple pie bite and then sprinkle with some cinnamon sugar. (1 tsp sugar + 1/4 tsp cinnamon)
Bake in the air fryer at 350 degrees F for 8-10 minutes or until the pastries start to brown on the top and the sides are bubbly. Serve warm.