Preheat oven to 350F. Butter the bottom and sides of a 9×13 inch metal baking pan. Put a long piece of parchment paper in the bottom of the pan, letting the parchment extend up two sides of the pan and overhang slightly on both ends. Place another piece of parchment paper in the same manner, perpendicular to the first sheet. (This will make it easy to remove the bars from the pan after they have baked.) Butter the parchment.
In a large bowl, whisk cocoa, espresso powder, and boiling water together in large bowl until smooth. Add unsweetened chocolate and whisk until chocolate is melted. Whisk in melted butter and oil. Add eggs, yolks, and vanilla extract and continue to whisk until smooth and homogeneous. Whisk in sugar until fully incorporated. Add flour and salt and mix with rubber spatula until combined.
Transfer the batter to prepared pan, smoothing the top. Bake 25 minutes. Remove from the oven and sprinkle the top with the peanuts and chopped peanut butter cups. Return to the oven and bake for 5 to 10 additional minutes or until toothpick inserted into the center comes out with just a few moist crumbs attached. Transfer pan to wire rack and cool 2 hours.
In a medium bowl, melt the chocolate chips, peanut butter and butter in microwave for 1 minute. Stir until smooth, microwaving for additional 30 seconds bursts until melted and smooth. Stir in the cereal to evenly coat. Evenly pour the mixture over top of the brownies. Spread to cover evenly. Refrigerate for 2 hours or until set. Using parchment overhang, lift brownies from pan. Cut into 2-inch squares and serve.