Preheat oven to 350 degrees F. Line a 9x13-inch baking pan with parchment or tin foil, leaving excess to hang around edges, and spray with nonstick cooking spray.
In a large bowl whisk the cocoa powder and espresso powder. In a small saucepan heat Kahlua just to a boil then pour over cocoa powder mixture. Whisk until smooth. Add unsweetened chocolate and whisk until melted and combined. Whisk in melted butter, vegetable oil, and 1/2 cup of the peanut butter. Whisk in eggs, vanilla, and sugar until smooth. With a rubber spatula fold in flour, salt, and chopped chocolate until just incorporated.
Pour batter into prepared pan. Heat the remaining 1/2 cup peanut butter in microwave for 15-20 seconds until loose and smooth. Drop dollops of peanut butter onto batter. Using a skewer or knife, swirl peanut butter into batter. Bake for about 30 minutes. Let cool completely on wire rack in pan before removing from pan and cutting into squares. Store at room temperature for up to 4 days.