Preheat your oven to 350°F (175°C). Line a 9x13 inch baking pan with parchment paper, leaving some overhang for easy removal later.
In a medium saucepan, melt the unsalted butter and 2 cups of semi-sweet chocolate chips together over low heat. Stir frequently until smooth and fully combined. Remove from heat and let cool slightly.
Once the chocolate mixture has cooled, whisk in the creamy peanut butter and brewed coffee until smooth.
Add the eggs one at a time, whisking well after each addition to achieve a nice, airy texture.
Stir in the granulated sugar and vanilla extract until fully incorporated.
Sift the unsweetened cocoa powder and optional instant espresso granules into the mixture. Fold gently until just combined.
Fold in the additional 1 cup of semi-sweet chocolate chips until evenly distributed throughout the batter.
Pour the brownie batter into the prepared pan. Drizzle the remaining 1/2 cup of creamy peanut butter over the top and use a knife to swirl it into the batter for a beautiful marbled effect.
Bake in the preheated oven for 25-30 minutes, or until the edges look set and a toothpick inserted into the center comes out with a few moist crumbs.
Allow the brownies to cool in the pan for at least 15 minutes before lifting them out using the parchment paper. Cut into squares and enjoy!