Preheat oven to 375° F. Line a cookie sheet with parchment paper and set aside.

To make the peanut butter filling, use an electric mixer to combine peanut butter and confectioners' sugar. Place in the freezer for 15 minutes to chill (it will be easier to handle later on). Meanwhile, make the chocolate cookie dough.

To make the chocolate cookie dough, whisk together flour, cocoa, baking soda and salt in a medium bowl. Set aside.

In the bowl of a stand mixer (or using a hand mixer), combine sugar, brown sugar, butter and peanut butter. Mix on medium-high until light and fluffy, about 2 minutes, scraping down the sides of the bowl when necessary. Add vanilla and egg, and mix until incorporated, about 30 seconds. With the mixer on low, slowly add the flour-cocoa mixture to the dough. Mix just until combined, about 30 seconds.

Scoop about a tablespoon of chocolate cookie dough, roll it into a ball and flatten it into a disc. Then scoop about a teaspoon of peanut butter filling and roll it into a ball. Place the peanut butter ball in the center of the chocolate disc and gently wrap the peanut butter inside the chocolate cookie dough. Roll into a ball and roll in the extra granulated sugar. Place on prepared cookie sheet and repeat with remaining dough.

Bake cookies for 8 to 10 minutes, or until the edges are set and the tops begin to crackle. Cool cookies on cookie sheet for 5 minutes, then transfer to a cooling rack to cool completely. Store in an airtight container at room temperature for up to 5 days.