Preheat oven to 350°F. Line a baking sheet with parchment paper or a silicon baking mat, set aside. Make the peanut butter cookie dough Using a stand mixer fitted with a paddle attachment, or a hand mixer, cream butter, peanut butter, brown sugar, and granulated sugar for 2-3 minutes. Add egg and vanilla and mix again until well combined. Add the salt, baking soda, and flour and mix until combined. Portion into heaping 2 tablespoon sized balls. Flatten slightly so they resemble a thick disk. Place on a wax paper lined plate and freeze for 10 minutes or until firm.
Make the brownie cookie dough Using a stand mixer fitted with a paddle attachment cream the butter, brown sugar, and sugar on medium speed for 1-2 minutes. Add the egg, corn syrup, and vanilla extract and mix until combined. Add the flour, cocoa, cornstarch, baking powder, baking soda, and salt. Mix until the dough comes together. Using a 1/3 cup, portion the dough into round balls. Use a tablespoon to create an indent in each brownie dough ball.
Take 1 frozen peanut butter disk and wrap the brownie cookie dough around it so that the peanut butter ball is now in the center and the brownie cookie dough is surrounding the entire peanut butter dough. Roll into a ball and place 6 balls on the baking sheet. Using the palm of your hand press down on each ball until it creates a thick disk, like a hockey puck.
Bake for 13-15 minutes or until edges are set and the tops appear sort of crackly. Do not overbake. Remove from the oven and cool on the pan for 10 minutes before transferring to a wire rack to cool completely.
Melt the toppings Melt the chocolate chips and 1 tsp of vegetable shortening in a microwave-safe bowl until smooth. Melt the peanut butter chips and 1 tsp vegetable shortening n a microwave-safe bowl until smooth.
Assembly Spread a 1-2 tablespoons of the melted chocolate overtop of each cookie. Then spread 1-2 tablespoons of the melted peanut butter chips over the chocolate. Use a toothpick to mix the two together. Enjoy warm or store in an airtight container for 3 days.