• Preheat oven to 350° Fahrenheit. Line 9x13 baking dish with parchment paper. Leave excess parchment paper slightly hanging over sides of baking dish, to help release brownies from dish after baking.

For the Blondie Layer

• Place butter in microwave-safe bowl and microwave in 30-second increments, stirring between each, until butter is melted but not boiling.
• Add melted butter, brown sugar, and white sugar to large mixing bowl. Whisk vigorously until ingredients are fully incorporated.
• Once combined, add 2 large eggs, 1 large egg yolk, and vanilla extract to bowl. Whisk until ingredients are fully incorporated into sugar mixture. Set bowl aside.
• Add flour, cornstarch, baking powder, and salt to medium mixing bowl. Stir or whisk to blend dry ingredients thoroughly.
• Working in gradual increments, add dry mixture into bowl with sugar mixture, stirring well after each addition to fully combine ingredients. Continue until all of dry mixture has been incorporated into wet mixture.
• Transfer prepared blondie batter to prepared baking dish. Spread batter out to cover entire surface of baking dish, making sure batter reaches all 4 corners of pan.
• Place baking dish in preheated oven. Bake, uncovered, 15 minutes or until edges of blondie layer are slightly set. Once edges are slightly set, remove baking dish from oven and set aside to cool 5 to 10 minutes.

For the Banana Pudding Layer

• While blondie layer bakes and cools, add room-temperature cream cheese and box of banana pudding mix to stand mixer bowl. Use stand mixer (or hand mixer) to whip ingredients together until fully combined, approximately 1 to 2 minutes on high speed.
• Once cream cheese mixture is smooth and fully combined, add 3 large eggs one by one. After adding each egg, beat mixture on low speed until egg is just incorporated before adding next egg.
• Once all eggs are fully incorporated and blondie layer has cooled, pour pudding mixture on top of blondie layer. Spread pudding mixture out into one even layer, covering blondies completely and reaching all 4 corners of baking dish.
• Place vanilla wafers on top of banana pudding layer in 3 rows of 5 cookies.
• Return baking dish to oven. Bake 20 minutes then begin checking doneness. Continue baking, checking brownies every 2 to 3 minutes, until pudding layer is mostly set and only slightly jiggly in center of pan. Note: depending on your oven and the type of pan you use, this step may take 20 to 30 minutes total.
• Carefully remove baked banana pudding brownies from oven and set baking dish aside. Let brownies cool completely.

To Serve

• When brownies are completely cooled, use excess parchment paper to lift brownies out of baking dish. Cut sheet of brownies into 15 squares and serve.