Preheat the oven to 350°.
Using a stand mixer, cream together the butter and sugars until light in color and fluffy in texture.
Add in the eggs, corn syrup and 1 tbsp of vanilla. Mix until thoroughly combined.
Next, add the flour, cocoa, cornstarch baking soda and salt. Mix until your chocolate cookie dough forms. The dough will be soft.
Fold in 1 1/2 cup of semi sweet chocolate chips.
Divide the dough out into 12 equal portions, I like to use my 1/2 cup measuring cup to help divide the dough. You'll want to use a little less than 1/2 cup of dough to have 12 cookies.
Roll each portion onto a ball then flatten slightly so it looks like a hockey puck before arranging on a parchment paper or silicone mat covered pan. Place 6 cookies per tray.
Bake at 350° for 15-17 minutes. The cookie should start to crack and crinkle, it will spread slightly and the centers of the cookie should no longer look wet before taking them out of the oven.
Once the cookies are out of the oven, make the buckeye peanut butter layer by first creaming together the butter and peanut butter.
Add the vanilla, milk and salt, mix until smooth.
Slowly add in the powdered sugar, mixing until all of the powdered sugar is incorporated. You will have a thick, peanut butter dough-like mixture.
Gather up the peanut butter mixture and form into a large log. Divide the mixture into 12 equal sections.
Take each section and roll into a ball and then flatten with the palm of your hands. Gently press the flattened peanut butter layer onto the center of each cookie while still warm.
Repeat with all cookies.
Melt the remaining 1 cup of chocolate chips in the microwave by heating the chips in a microwave safe bowl for 30 seconds at a time, stirring after each 30 seconds, until the chocolate is melted.
Spoon the melted chocolate on top of the peanut butter layer, repeat with the remaining cookies.