In a medium-sized bowl, sift together flour, cocoa powder, cream of tartar, baking soda and salt.

In a large mixing bowl, beat butter and granulated sugar until light and fluffy. Add eggs, one at a time, and mix well. Add vanilla, vinegar and red food coloring and mix well. Slowly add flour mixture and beat on low speed until dough is thoroughly mixed.

The dough will be very soft at first. Cover and chill for at least two hours or, even better, overnight.

Preheat oven to 350°F (175°C). Line baking sheets with parchment paper.

Form 1-inch (2.5 cm) balls of dough and roll them in powdered sugar. Place on the baking sheet, leaving plenty of room in between.

Bake cookies for 10-12 minutes, just until they no longer look shiny & gooey in the center. Be careful not to overbake the cookies or they will dry out.

Remove cookies from the oven and allow them to stand on the baking sheets for about 5 minutes to harden slightly. Using a spatula, remove cookies from the baking sheets and place them on cooling racks to cool completely.

Store cookies in an airtight container.