Preheat the oven to 350°F (180°C). Line a baking tray with parchment paper. Set aside.
Add softened butter and brown sugar to the bowl of your stand mixer and cream them together until smooth.
Add egg, vanilla extract and peanut butter and mix in.
Now add the all purpose flour, cocoa powder, baking soda and salt and stir it in by hand (with a spoon, but just don't use your electric mixer for this part) into a thick cookie dough.
Break off pieces of the dough and roll into balls and place them evenly on your prepared baking tray. Aim for 20 cookies. The balls are quite large.
Flatten with a fork and then place into the oven to bake for 12 minutes.
Leave them to cool on the tray and when cool, melt the peanut butter in the microwave and then drizzle it over cooled cookies.
Let the cookies sit for around 10 minutes for the peanut butter to harden and then enjoy!