For filling, stir together peanut butter and powdered sugar in a medium bowl until smooth. (The peanut butter mixture is quite thick, you may need to use your hands to knead it together.) Cover and place in the freezer while you prepare the dough.

Preheat your oven to 350 degrees and line cookie sheets with silicone liners or parchment paper.

In a large mixing bowl, beat sugars, butter, and peanut butter until creamy. Beat in vanilla, egg, and yolk till well combined.

Sift in the flour, cocoa, baking soda, and salt. Stir till well mixed.

Take a heaping tablespoon of dough and roll it into a ball. It should weigh about an ounce. Repeat with the remaining dough. You should end up with 24-26 balls.

Remove the filling from the freezer and roll it into little balls. Make sure you have the same number of filling balls and chocolate dough balls!

To make cookies, take a chocolate dough ball and flatten it out in the center of your palm. Place a ball of filling in the center of the dough. Wrap the dough around the PB filling and pinch together to seal. Roll the ball in your hand to smooth it out.

Repeat with the remaining dough and filling.

Roll the cookie dough balls in sugar and place them on silicone-lined or lightly greased cookie sheets at least 2 inches apart. Flatten slightly with the palm of your hand.

Bake at 350° for 9-10 minutes. Transfer cookies to a wire rack to cool completely.