• Preheat the oven to 350°F and prepare an 8x8-inch baking dish by lining it with parchment paper (or lightly grease and flour). (You could use a 9x13-inch baking dish for more servings, but the bars will be thinner.)
• Using a whisk, combine the melted butter and brown sugar in a large bowl. Mix well.
• Add the eggs and the egg yolk, one at a time, stirring well after each addition, scraping the sides of the bowl as needed.
• Whisk in the vanilla extract.
• In a separate, medium-sized bowl, whisk together the flour, cornstarch, baking powder, and salt.
• Using a rubber spatula, gradually stir the flour mixture into the butter and egg mixture until completely combined.
• Fold in diced apples.
• Spread the batter evenly into the prepared pan.
• Bake for 50-55 minutes, or until the edges just begin to turn golden brown and there is no jiggle in the bars. (If you are using a 9x13-inch pan, bake for about 45 minutes.)
• Allow blondies to cool before topping with maple glaze.

Maple Glaze

• Melt the maple syrup and butter over medium-low heat and whisk until fully incorporated.
• Remove from heat and add the confectioners' sugar, whisking to combine.
• Drizzle over the cooled blondies. Cut and serve.