In a large mixing bowl cream together butter, oil, and sugars until
light and fluffy. Add eggs, vanilla, and salt and mix until combined.
Add in the baking soda and cornstarch and half of the flour and mix
well. Pour in the remaining flour and mix only until combined. Stir
in chocolate chips and cover and chill for one hour.
Preheat oven to 350
Drop heaping spoonfuls of dough onto ungreased cookie sheets,
making sure the piles of dough are nice and tall. if using a cookie
scoop, scoop one ball of dough right on top of another one. This is
what makes the cookies thick!
Bake 7-8 minutes for medium sized cookies or 10 minutes for large
cookies. Pull them from the oven when the edges are slightly
golden and the centers look just barely done. After 2 minutes
remove cookies from sheets onto cooling racks.
Store in an airtight container at room temperature