1. Cream together butter, shortening, and both sugars. Stir in eggs and vanilla until well combined.

2. In a separate bowl, stir together flour, baking soda, and salt. Mix thoroughly, and add to the sugar mixture. Stir gently just until everything is combined. Don't over-mix. Fold chocolate chips into the dough until evenly dispersed. 

3. Place dough in an airtight container and refrigerate for at least three hours, up to two days. 

4. Roll cookies into 1 inch balls and bake at 375 degrees for 7 minutes. Turn the tray in the oven and bake for an additional 1 to 1 1/2 minutes, depending on how they look. The bottom edges should look golden and baked through, the tops should look pale, but not doughy. Remove tray from oven and set on a cooling rack. Allow the cookies to remain on the tray for an additional 3 minutes before transferring to the cooling rack. If cookies look brown all over, skip this step and transfer to a cooling rack immediately. 

Note: Freeze dough by rolling it into balls first. You can bake them directly from the freezer like this, increasing baking time by 30 seconds to 1 minute.

This recipe makes quite a lot, as it's technically a double batch. It can be halved if you don't need 72 cookies, although I don't know anyone who has ever experienced that!