In large bowl, beat the butter, oil and sugars. Beat in eggs until well blended. Beat in vanilla. Combine the flour, baking soda and cream of tartar; gradually add to creamed mixture.

Drop by small teaspoonfuls onto ungreased baking sheets. Bake at 375° for 8-10 minutes or until lightly browned. Remove to wire racks to cool.

Preheat oven to 375°.

Yield: about 5 dozen.