Pre heat oven to 175°Celsius. Prepare baking trays lined with parchment paper.
Sieve flour, cocoa powder, salt, baking powder and baking soda together and keep them aside.
In a clean bowl, cream butter, peanut butter and both the white and brown sugars until creamy. Add the egg and continue beating until it is well incorporated.
Next, add vanilla extract and beat for about 15 seconds, followed by the sifted dry ingredients. Mix until all the ingredients are well incorporated, and the dough comes together, soft. Set aside.
To make the filling, sift cocoa powder and powdered sugar into a bowl.
Add the peanut butter and mix until the filling comes together.
Using a 1 teaspoon measuring spoon, scoop the filling out onto a plate. Shape each scoop into a round ball before placing them in the fridge to chill.
To assemble the cookies, scoop 1 tablespoon of cookie dough, form it into a round ball and make a deep dent in the center. Place one chilled filling ball in the center and cover the dent by pinching the cookie dough together.
With very light pressure, roll the cookie in your palms until its round. Place on a lined baking tray and flatten slightly with your fingers. Repeat the process until all the cookies are done.
Bake the cookies for 9 minutes at 175°Celsiuc. Once baked, let them cool slightly on the baking tray before transferring them into a wire rack to cool completely.
Place cooled cookies in an airtight container. The cookies can last up to 2 weeks if stored properly.