Preheat the oven to 350, and position a rack in the center of the oven. Line a cookie sheet with parchment paper.
In a medium-sized bowl, add the butter, cream cheese and 1/2 cup of the sugar. Beat with an electric mixer on HIGH until well-mixed and fluffy, about 1 minute. Next, beat in the egg until just combined.
In a small bowl, stir together the flour, cream of tartar, baking soda and salt. Sprinkle this mixture over the butter mixture, and beat until just combined.
In a shallow bowl, add the remaining 2 tablespoons of sugar and cinnamon. Stir together.
Scoop 12 balls of dough into small balls and roll into the cinnamon-sugar mixture.
Place the dough balls evenly on a baking sheet. Bake for 10-12 minutes.
Let cool on a baking sheet for 1 minute before moving to a wire rack to cool completely.