Step 1

Preheat the oven to 375 degrees F.

Step 2

In a large bowl, beat the butter, the oil, the sugar, and the confectioners' sugar.

Step 3

Beat the eggs into the sugar mixture until well-blended.

Step 4

Beat the vanilla into the egg mixture.

Step 5

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

Step 6

Gradually add the flour mixture into the egg mixture.

Step 7

Drop the dough in small teaspoon-sized clumps onto ungreased baking sheets.

Step 8

Bake until the cookies are lightly browned, about 8-10 minutes.

Step 9

Transfer the cookies to wire racks to cool.

Step 10

Serve.