Combine flour, unsweetened cocoa powder, baking soda, and salt in a bowl and stir to combine. Set aside.
In a separate bowl, combine the brown sugar, white sugar and melted butter. Stir the mixture until just combined and no chunks of brown sugar remain. In the same bowl add the eggs, vanilla extract, Karo® Corn Syrup and stir until combined.
Add the dry ingredients into the large bowl and stir until combined. The dough will be sticky and the consistency in-between brownie batter and cookie dough. Stir in the chocolate chunks until evenly distributed.
Line a baking sheet with parchment paper. Take a heaping tablespoon of the cookie dough and place it on the prepared baking sheet. I like to do 12 cookies per baking sheet leaving about 2 inches in between each ball of cookie dough. You can use one sheet and cook two batches of cookies, or use two baking sheets and bake them on separate racks.
Once the sheet(s) is filled, place in the oven at 350 degrees F for 9-11 minutes. The cookies will be soft on the tops still, but firm on the bottom when finished. Remove the baked cookies from the sheet and place on a cooling rack. Enjoy warm or store leftovers for up to 2 weeks. Enjoy!
Leftover Storage: Store leftover cookies in a airtight container or storage bag at room temperature for up to 2 weeks. Enjoy at room temperature or warm in the microwave for 10 seconds to enjoy warm.
Make Ahead Instructions: You can make the dough up to 24 hours ahead of time and store it in the fridge covered. Follow the recipe instructions, but do not place the dough on the baking sheets, just leave it in the bowl. Store the raw cookie dough in the fridge for up to 1 day. When ready to bake, let the dough come to room temperature then follow the recipe instructions for baking the cookies.