Preheat your oven to 350°F (175°C). In a medium bowl, whisk together the all-purpose flour, unsweetened cocoa powder, baking soda, and salt. In a separate large bowl, cream together the room temperature unsalted butter, granulated sugar, and brown sugar until light and fluffy. Beat in the egg and vanilla extract until well combined. Gradually add the dry ingredients to this mixture, stirring until just combined.

Drop dollops of creamy peanut butter over the surface of your chocolate dough. Using a knife or a skewer, gently swirl the peanut butter into the dough to create marbled patterns, being careful not to overmix.

Cover the bowl with plastic wrap and chill the dough in the refrigerator for at least one hour.

Line your baking sheets with parchment paper. Scoop tablespoonfuls of dough onto the prepared sheets, leaving space between each scoop. Bake for about 10-12 minutes or until cookies are set but still soft in the middle.

Let the cookies cool on the baking sheet for about 5 minutes before transferring them to a wire rack to cool completely.