Instructions

• Preheat the oven to 350°F. Line a 9×13" pan with foil and spray the foil with nonstick cooking spray (leave some foil overhang to lift the bars out later).
• In a large bowl using a hand mixer or in the bowl of a stand mixer fitted with the paddle attachment, beat the softened unsalted butter and the peanut butter together until smooth.
• Add the packed brown sugar and beat until the mixture is creamy and combined.
• Add the egg, vanilla extract, milk, salt, and baking soda; mix until everything is incorporated.
• Gradually add the all-purpose flour and mix on low speed (or stir) until just combined and no large streaks of flour remain.
• Fold in the peanut butter chips, chocolate chips, and chopped Butterfinger pieces until evenly distributed through the dough.
• Transfer the dough to the prepared 9×13" pan and press it into an even layer using a spatula or your hands. If you like, sprinkle additional peanut butter chips and Butterfinger pieces over the top.
• Bake in the preheated oven for 20–25 minutes, or until the edges are golden brown and the center is set (a toothpick inserted near the center should come out with a few moist crumbs, not wet batter).
• Remove the pan from the oven and cool completely in the pan on a wire rack. Use the foil overhang to lift the bars from the pan, then slice into bars.
• Store cooled bars in an airtight container for up to 3 days, or freeze for up to one month.