Step 1

Preheat the oven to 375 degrees Fahrenheit.

Step 2

In a large bowl, beat butter, oil, and sugars with an electric mixer.

Step 3

Add the eggs and beat until well-combined. Stir in the vanilla.

Step 4

In a separate bowl, sift in the flour, baking soda, and cream of tartar.

Step 5

Gradually add the dry ingredients to the butter mixture. Gently mix until combined.

Step 6

Drop teaspoonfuls of cookie dough onto ungreased cookie sheets. Bake for 8 to 10 minutes, or until cookies have slightly browned.

Step 7

Transfer the cookies to wire racks and allow to cool. Enjoy!