Preheat oven to 350°F. Line a baking sheet with parchment paper, set aside.
Place a piece of wax paper on a plate. Use a 1 tablespoon sized cookie scoop or a spoon, to portion the hot fudge onto the plate. Freeze for 10-20 minutes or until cold. This will help the hot fudge not be so sticky, and makes it easier to stuff the cookies.
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 eggs, corn syrup, and vanilla extract and mix until combined. Use a rubber spatula to scrape down the sides of the bowl.
Add the flour, cocoa, cornstarch, baking soda, and salt. Mix until the dough comes together.
Using a ¼ cup measuring spoon portion the dough into round balls. Using a tablespoon, press an indentation into each ball. Fill the indent with a frozen hot fudge, and gently wrap the cookie dough around the hot fudge.
Place 6 hot fudge filled cookie dough balls on a baking sheet. Using the palm of your hand press down on each ball until it creates a thick disk.
Bake for 10-11 minutes or until edges are set and the center is no longer shiny.
Remove from oven. Let cookies cool on the baking sheet for 5-10 minutes before transferring to a wire rack.
Dust each cookie with some powdered sugar and enjoy warm or at room temperature.