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 the 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.
While the cookies are cooling, make the frosting, by whipping the butter and cream cheese until smooth.
Add the powdered sugar, one cup at a time, mixing until it is combined before adding another cup.
Add in the cocoa powder andthe vanilla.
Add milk 1 tsp at a time until you've reached your desired consistency.
Add the frosting to a piping bag fit with a large closed star (2D) tip. Pipe the frosting onto the warm cookies in a spiral, starting in the center of the cookie working your way out.
Serve warm.