1. Preheat your oven to 350°F (175°C) and line a 9×13-inch baking pan with parchment paper, leaving some overhang for easy lifting.
2. In a medium bowl, mix together the cocoa powder, flour, baking powder, salt, and espresso powder until well blended. Set aside.
3. Place the butter and sugar in a large saucepan over medium heat. Stir as the butter melts and bring the mixture to a gentle simmer. Continue cooking for about 2 minutes until the temperature reaches approximately 230°F, stirring occasionally.
4. Remove the pan from the heat. Add the chocolate chips and vanilla extract, stirring until the chocolate melts into the mixture. Let it cool for around 10 minutes.
5. Beat in the eggs one at a time, mixing well after each addition until the batter looks glossy and smooth.
6. Gradually fold the dry ingredients into the chocolate mixture. Stir just until combined. The batter will be thick and rich.

Assembling the Layers

1. Spread half of the brownie batter evenly into the prepared baking dish.
2. Gently layer the peanut butter over the top, smoothing it out as best as possible. Spoon or pipe the marshmallow creme over the peanut butter layer.
3. Cover everything with the remaining brownie batter, spreading it carefully to seal the filling.
4. Bake for 28 to 30 minutes, or until the top is set and a toothpick inserted comes out with a few moist crumbs.
5. Let the brownies cool completely in the pan before slicing to ensure clean layers and perfect texture.