• Preheat the oven to 350°F and line 2 baking sheets with parchment paper.
• Cream the butter, brown sugar, and granulated sugar in a stand mixer on high until smooth, scraping down the sides of the bowl as needed.
• Add the eggs, vanilla extract, and corn syrup, and mix until combined.
• Add the flour, cocoa powder, baking soda, cornstarch, and salt. Mix on low speed until a thick dough forms.
• Fold in the chocolate chips.
• Scoop the dough onto the prepared baking sheets with a 1-tablespoon cookie scoop or use a spoon, and bake for about 10 minutes or until the centers are set.
• Cool the cookies completely on a wire rack before frosting.

To make the frosting:

• Beat the butter and cream cheese in the bowl of a stand mixer fitted with the paddle attachment on high until smooth. Add the cocoa powder, vanilla extract, and powdered sugar, and beat until fluffy. Add a teaspoon of water if your frosting is too thick.
• Pipe frosting onto the cooled cookies and serve.