Preheat your oven to 350°F (175°C) and line two baking sheets with parchment paper.

In a medium bowl, whisk together the all-purpose flour, cocoa powder, baking soda, and salt. In a larger mixing bowl, cream the unsalted butter with granulated sugar and brown sugar until fluffy. Add the egg and vanilla, mixing until incorporated. Fold the dry ingredients into the wet ingredients until no dry streaks remain.

In another bowl, whisk together the flour, baking soda, and a pinch of salt for the peanut butter dough. In a larger bowl, cream the unsalted butter with peanut butter, granulated sugar, and brown sugar until smooth. Add the egg and vanilla, blending well. Combine dry ingredients until just mixed.

Take equal portions of the chocolate dough and peanut butter dough, rolling into 1 tablespoon-sized balls. Place on lined baking sheets, spaced to allow for spreading.

Bake cookies for 10-12 minutes until edges are set and centers are slightly underbaked. Cool on baking sheets for 5 minutes.

Transfer cookies to a wire rack to cool completely.