Preheat the Oven: Start by preheating your oven to 350°F (175°C) and lining a baking sheet with parchment paper.
Mix the Wet Ingredients: In a medium-sized bowl, whisk together the melted butter and granulated sugar until smooth. Add the eggs, one at a time, mixing well after each addition, followed by the vanilla extract.
Combine Dry Ingredients: In another bowl, sift together the flour, cocoa powder, and salt. Gradually add the dry ingredients to the wet mixture, stirring until well combined.
Add the Peanut Butter: Stir in the peanut butter until fully incorporated. If you want to add chocolate chips for extra indulgence, fold them in now.
Swirl the Peanut Butter: Using a spoon or spatula, dollop additional peanut butter on top of the cookie dough, and gently swirl it through with a knife to create a marbled effect.
Scoop the Dough: Using a cookie scoop or tablespoons, drop dough onto the prepared baking sheet, leaving space between each cookie to allow for spreading.
Bake: Place the baking sheet in the preheated oven and bake for 10-12 minutes. The cookies will look slightly underbaked in the center—this is perfect for that chewy texture!
Cool and Enjoy: Let the cookies cool on the baking sheet for a few minutes before transferring them to wire racks to cool completely.