Lightly grease an 8 inch square, 9 inch square, or 6x9 inch baking dish using butter spray, butter or crisco shortening. You can also line the dish with aluminum foil or parchment paper. Set aside.

In your stand mixer or handheld mixer, cream the brown sugar, powdered sugar, 5 tbsp butter, and peanut butter together, until smooth. This should take several minutes in a stand mixer set to medium. Press the peanut butter mixture into prepared pan, ensuring you fill to the corners.

In a medium-size microwave-safe bowl, melt the milk chocolate chips and remaining 5 tbsp butter in 30-second increments, stirring after every 30 seconds with a spoon. I only needed to cook mine for two sets of 30 seconds.

Pour melted chocolate/butter mixture over peanut butter layer. Spread out evenly with a spatula.

Cover dish with plastic wrap and place in the refrigerator for at least 3 hours, or until completely firm. I let our's chill overnight, and it was perfect.

Let the bars sit at room temperature for about 10 minutes to make the cutting easier. I used a small metal spatula to cut and serve and it worked perfectly.