Preheat your oven to 350°F (175°C). This ensures that your brookies bake evenly.
In a microwave-safe bowl, combine the semi-sweet baking chocolate with a tablespoon of peanut butter. Heat in the microwave in 20-second intervals, stirring in between, until melted and smooth.
In a separate large mixing bowl, combine the peanut butter and granulated sugar. Mix until well combined.
Crack one egg into the peanut butter-sugar mixture, and add the vanilla extract. Stir until fully incorporated. Reserve the other egg for later.
Pour the melted chocolate mixture into the peanut butter mixture and stir until everything is combined.
Add the sweetened condensed milk to the mixture and mix until smooth.
Beat the remaining egg in a small bowl, then fold it into the batter until combined.
Grease your 9x9 inch baking pan lightly with cooking spray or line it with parchment paper for easy removal.
Pour the batter into the prepared baking pan and spread it evenly.
If desired, sprinkle the chopped peanuts on top of the batter for added crunch.
Bake in the preheated oven for 25-30 minutes, or until the edges are set and a toothpick inserted in the center comes out with a few moist crumbs.
Allow the brookies to cool in the pan for about 10 minutes before transferring them to a wire rack to cool completely. Once cool, slice them into squares and enjoy!