Add melted butter, graham cracker crumbs, brown sugar, sifted powdered sugar and peanut butter to a large mixing bowl.

Using an electric mixer, combine until all ingredients are completely incorporated

Line a 9 x 13 pan with parchment paper and drop in your peanut butter batter

Spread the batter out evenly with hands or spatula

In a microwave safe dish, add in the semi-sweet chocolate and butter along with the espresso powder if using it

Microwave for 2 minutes, stopping after each 30 seconds to stir

When the chocolate is completely melted, pour on top of the peanut butter batter and then spread the chocolate out evenly

Refrigerate for 3 hours or even overnight