1. Combine all of the peanut butter filling ingredients in a medium bowl

2. Spoon 18 even dollops of the mixture onto a lined chopping board or baking tray

3. Freeze for 1 hour to overnight

4. In a large mixing bowl, cream the butter and both sugars until light and fluffy

5. Add the egg, egg yolk, and vanilla, and beat again until smooth

6. In a separate medium bowl, sift and whisk together the flour, cocoa powder, cornstarch, baking powder, baking soda, and salt

7. Gradually add the dry ingredients to the wet and fold together using a spatula until just combined

8. Fold the dark chocolate chips into the mixture (try not to overmix)

9. Cover the dough with plastic wrap and chill for 30 minutes

10. Scoop medium-sized balls of the cookie dough into your hand and gently roll between your palms to create a smooth ball

11. Using your thumb, press a crater into the center (don’t press too deep)

12. Retrieve one dollop of the peanut butter filling and press it into the crater, then fold the dough over the peanut butter filling so there is no filling showing

13. Roll the cookie dough gently between your palms to create a smooth ball (make sure all the peanut butter filling is covered)

14. Refrigerate the cookie balls for 30-45 minutes

15. Preheat the oven to 190°C and line 2 baking trays with parchment paper

16. Place the cookies onto the lined baking trays, evenly spaced

17. Bake for 10-13 minutes

18. Allow the cookies to cool

19. Enjoy!