• Preheat the oven to 350°F and prepare a 9x9-inch pan by lining it with parchment paper (or lightly grease and flour). (You could use a 9x13-inch pan for more servings, but the bars will be thinner.)

Blondies

• Whisk melted butter and brown sugar in a large bowl until fully incorporated.
• Add the eggs and the egg yolk, one at a time, whisking well after each addition.
• 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. Set aside as you prepare the cinnamon-sugar layer.

Cinnamon Layer

• In a small bowl combine melted butter, brown sugar, and cinnamon. Mix well.

Assembly

• Spread half the blondie batter into the bottom of the lined baking dish. (The batter is thick.)
• Evenly spread the cinnamon layer over the blondie batter.
• Add the remaining blondie batter on top, spreading it out to the edges of the pan.
• Bake for 35-38 minutes, or until the edges just begin to turn golden brown and the center is no longer jiggly.
• Allow the bars to cool completely before adding the cream cheese frosting.

Whipped Cream Cheese Frosting

• Put cream cheese, butter, confectioners sugar, vanilla, and salt in a stand mixer fitted with the paddle attachment.
• Mix on low until just combined. Once ingredients are all incorporated, turn the mixer on high and leave it for 4-5 minutes. Frosting should be light and fluffy.
• Spread frosting over cooled blondies.