Preheat oven to 350°F and line baking sheets with parchment paper.
In a large bowl, cream together butter, granulated sugar, brown sugar, and ½ cup peanut butter until light and fluffy.
Beat in eggs one at a time, then add vanilla extract and mix well.
In a separate bowl, whisk together flour, cocoa powder, baking soda, and salt.
Gradually add dry ingredients to wet ingredients, mixing until just combined. Fold in chocolate chips.
Scoop about 2 tablespoons of dough and flatten slightly. Press a mini Reese's cup into the center and wrap dough around it, rolling into a ball.
Place cookies on prepared baking sheets, spacing 2 inches apart.
Bake for 9-10 minutes until edges are set but centers are still slightly soft. Don't overbake!
Let cool on baking sheet for 5 minutes, then transfer to a wire rack to cool completely.
For the peanut butter drizzle, microwave ½ cup peanut butter for 20 seconds until slightly melted. Stir in powdered sugar until smooth, then drizzle over cooled cookies using a fork or piping bag.