Add butter to large saucepan. Turn on medium heat. Once melted, butter will start to foam. Browned bits will be seen at the bottom of the pan once it is browned. Remove from heat and set aside until ready for use.
Preheat oven to 350°. Line the 9x13 cake with with parchment paper, leaving an overhang on both sides (makes it easier to lift blondies out). Set aside. Peel and chop 2 apples.
In a large saucepan, add apples, maple syrup, and cinnamon. Stir apple mixture over medium heat until the apples have softened slightly. Set aside.
Whisk flour, salt, cinnamon, nutmeg, and baking powder in a large mixing bowl. Set aside.
In another mixing bowl, cream together the butter, brown sugar, eggs, and vanilla extract together.
Add the wet ingredients into the dry ingredients and mix until well combined. Fold in the apples (batter will be thick and that is ok).
Transfer batter and spread evenly into prepared cake pan. Bake for 30-35 minutes or the top is slightly golden brown or a toothpick inserted into the center comes out with moist crumbs.
Remove from oven and let blondies cool completely. Once cooled, lift blondies out of the pan and cut.