Prepare a baking sheet by lining it with a silicon mat or a sheet of parchment paper, then set aside. This is important for these cookies, because they will otherwise stick to the cookie sheet.
Using either a stand mixer or an electric hand mixer, cream together the butter, brown sugar and granulated sugar until light in color and fluffy in texture. (Approximately 2-3 minutes).
Scrape the sides of the bowl and add in the egg, corn syrup and molasses. Mix until well combined.
Next, add in the dry ingredients: flour, salt and baking soda. Mix until a sticky dough forms. Emphasize on the sticky-sticky! This will not feel like your normal cookie dough because of all of that corn syrup.
Finally, stir in the chocolate chunks until fully incorporated. Be sure not to overmix.
Portion out your dough into 3 tbsp portions using a cookie scoop (#24) or your hands. Shape the dough into a ball and arrange them on your cookie sheet.
Bake your cookie dough at 350° F for 9-11 minutes. You will know the cookies are done when they start to spread and the edges begin to turn golden brown.
Allow the cookies to cool on the pan before transferring to a wire rack.
To get the soft edge that Costco cookies are known for, store the cookies in an airtight container overnight. This waiting period helps the edges to soften. If you can’t wait and need to eat them right out of the oven, the edges will be a little buttery and crisp.