Preheat your oven to 350°F (175°C). Line an 8x8-inch baking pan with parchment paper, leaving some overhang for easy removal later.
In a large mixing bowl, combine the unsalted butter, light brown sugar, and granulated sugar. Use a whisk or electric mixer to cream them together until the mixture is light and fluffy.
Add the large egg and egg yolks to the butter mixture, followed by the creamy peanut butter and vanilla extract. Mix until fully incorporated.
In a separate bowl, whisk together the all-purpose flour, baking soda, cocoa powder, and salt. Gradually add this dry mixture to the wet ingredients, stirring gently until just combined.
Carefully fold in the chopped salted or candied peanuts until evenly distributed throughout the batter.
Pour the brownie mixture into the prepared baking pan and spread it evenly. Bake in the preheated oven for 25-30 minutes, or until the edges are set and a toothpick inserted in the center comes out mostly clean.
Allow the brownie bars to cool in the pan for about 10 minutes before lifting them out using the parchment overhang. Transfer to a wire rack to cool completely before slicing into bars.
