- In a medium bowl, stir together flour, cream of tartar and baking soda.
- In a large bowl, beat the butter and shortening until fluffy. Gradually beat in powdered sugar and vanilla extract.
- Then beat in the eggs, one at a time. Gradually fold in the flour mixture until well blended.
- Cover the bowl with plastic wrap. Refrigerate at least 4 hours.
- Preheat oven to 350 F. On a lightly floured surface, roll out a portion of the dough into 1/8 inch thickness, keep remaining dough chilled until ready to use.
- Cut out cookies with a floured cookie cutter.
- Place cookies 1 inch apart on kitchen parchment paper covered baking sheets.
- Sprinkle with colored sugar or candies as desired or leave plain to frost. Bake for 8 to 11 minutes or until set but not browned. Transfer to wire racks to cool then serve!