1. Preheat the oven to 400 degrees. In a medium-sized bowl, sift the flour, cream of tartar, baking soda and salt. In a large bowl, cream the butter and 3/4 cup of sugar. Beat in the egg. One third at a time, stir in the dry ingredients until thoroughly mixed.
2. Pinch off small pieces of dough and roll into marble-size balls (a fun job for kids). On a plate or in a shallow bowl, mix the cinnamon-sugar mixture, roll the ball in the cinnamon-sugar mixture and place on an ungreased cookie sheet 2 inches apart. Flatten with the bottom of a glass. Bake for 6 to 10 minutes, or until the edges lightly brown. Transfer the cookies to a cooling rack. When they're thoroughly cool, store in an airtight jar. Makes 10 to 12 dozen cookies.