Line a 13x9-inch baking pan with foil, allowing some to overhang the edges, and lightly grease the foil with cooking spray.
In an extra-large mixing bowl, beat the creamy peanut butter and softened butter with an electric mixer on medium speed until smooth.
Add the packed brown sugar and vanilla extract; beat until combined, scraping the bowl as needed.
Add the eggs and beat for 3 minutes or until the mixture is light and fluffy.
In a medium bowl, stir together the all-purpose flour, finely crushed cornflakes, baking powder, and salt.
Add this dry mixture to the peanut butter mixture and beat until well combined.
Spread half of the batter in the prepared pan.
Arrange the broken candy bar pieces on top of the batter.
Spread the remaining batter over the candy layer.
Bake for 25 to 28 minutes or until the top appears dry.
Allow it to cool in the pan on a wire rack.
If desired, drizzle the bars with melted chocolate.
Using the foil overhang, lift out the uncut bars and then cut them into individual bars.
Notes / Tips / Wine Advice:
This recipe yields approximately 48 servings, each consisting of one bar.To Store:Layer the bars between sheets of waxed paper in an airtight container. Store them in the refrigerator for up to 3 days or freeze them for up to 3 months. Enjoy!