Melt the 1/2 cup butter and let cool to room temperature.
Add in the brown sugar, egg and vanilla. Mix well.
In a separate bowl mix together the flour, baking powder, salt and cinnamon
Add the dry ingredients to the wet ingredients and mix until just combined.
Fold in the diced apples and chopped walnuts.
Spread the batter into a 9x9 baking pan and bake at 350 for about 25 minutes.
While the blondies bake make the glaze. Brown the 1/4 cup butter and pour into a medium bowl.
Add in the icing sugar, cinnamon and salt. Whisk until smooth.
Remove the blondies from the oven when done. Let cool.
Drizzle the blondies with the glaze and sprinkle with the finely chopped walnuts.