Step 1

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.)

Step 2

Using a whisk, combine the melted butter and brown sugar in a large bowl. Mix well.

Step 3

Add the eggs and the egg yolk, one at a time, stirring well after each addition, scraping the sides of the bowl as needed.

Step 4

Whisk in the vanilla extract.

Step 5

In a separate, medium-sized bowl, whisk together the flour, cornstarch, baking powder, and salt.

Step 6

Using a rubber spatula, gradually stir the flour mixture into the butter and egg mixture until completely combined.

Step 7

Fold in diced apples.

Step 8

Spread the batter evenly into the prepared pan.

Step 9

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.)

Step 10

Allow blondies to cool before topping with maple glaze.

Step 11

Melt the maple syrup and butter over medium-low heat and whisk until fully incorporated.

Step 12

Remove from heat and add the confectioners' sugar, whisking to combine.

Step 13

Drizzle over the cooled blondies. Cut and serve.