Preheat oven to 375°. Prepare baking sheets by lining with parchment paper or use silicone baking mats.
In the bowl of a standing mixer, cream together the shortening, softened butter, and sugars until creamy and smooth (do not over mix). Next, mix in the eggs, egg yolk, and vanilla just until combined.
In a separate bowl, combine the flour, corn starch, baking soda, and salt. Mix well. Add the dry ingredients to the wet; and mix on a low setting, just until fully incorporated. Add one 12-ounce bag of chocolate chips, and mix in by hand with a wooden spoon, just until evenly incorporated.
Using a 1 ½ tablespoon cookie scoop, place cookie dough on prepared baking sheets, two inches apart. Bake for 10-11 minutes or until the edges are golden brown.
Take the cookies out of the oven and allow them to rest for 2 to 3 minutes, then move to a cooling rack to completely cool. **If you want to garnish the tops of the cookies with additional chocolate chips, do so immediately after taking them out of the oven. Allow the pans to come to room temperature before placing more cookie dough on them. **For a quicker method of cooling your pans, run them under cool water for 20 to 30 seconds, dry and continue with your baking. Repeat the process for the remaining cookies.
Store in an airtight container for 4 to 5 days.