In a non-stick skillet, over medium heat, melt the butter, brown sugar, and cinnamon together until bubbly, about 1 minute.
Add the diced apples. Stir and cook over medium heat for 4-6 minutes or until softened, but still firm. Once cooked, transfer apples to a bowl to cool slightly.
Make the Blondies:
Preheat the oven to 350ºF, and line a 9×13-inch baking dish with parchment paper. Spray with nonstick cooking spray; set aside.
In a medium bowl, whisk the butter, brown sugar, eggs, and vanilla until smooth. Switch to a wooden spoon, add the flour and baking powder, and stir until just combined. Gently fold in the walnuts, white chocolate chips, and caramelized apples.
Pour batter into prepared pan, spreading evenly with a rubber spatula. Bake for about 22-25 minutes, or until edges are firm and golden and the top is set; do not overbake. Blondies firm up as they cool.
Make the Glaze:
In a medium bowl, whisk the powdered sugar and 2 Tablespoons of apple cider together until smooth. Add more apple cider to reach desired thinness/consistency.
Drizzle glaze over the cooled blondies. Slice into squares and enjoy!
Notes
*I dissolved one packet of Alpine Spice original instant apple cider in 1/2 cup of hot water. I used half the amount of water called for to achieve a stronger flavor.