Preheat the oven to 375°F. Line two baking sheets with parchment paper and set them aside.
In the bowl of a standing mixer, beat together butter, vegetable oil, granulated sugar, and powdered sugar.
Add the eggs and vanilla and beat for 2 minutes longer, scraping down the sides of the bowl as needed.
Mix together flour, baking soda, and cream of tartar in a separate bowl.
With the mixer running on low speed, add the flour mixture a couple of spoonfuls at a time until the dough is evenly combined.
Use a cookie dough scoop to drop spoonfuls of the dough onto prepared baking sheets. Bake for 7 to 8 minutes until just lightly golden brown on the bottom edges.
SEVENTH STEP: Transfer baked cookies to cooling racks.