Preheat the oven to 350 F. In a medium bowl, whisk together flour, salt, baking soda, and cream of tartar. In a large bowl, combine butter with sugar until fluffy.
Add in the egg and vanilla extract, and mix until smooth. Add in the flour mixture, mix until it is fully combined. Fold in the Christmas sprinkles. In a small bowl, combine granulated sugar and ground cinnamon.
Evenly press the cookie dough into a greased 8-inch square baking dish. Sprinkle the cookie bars with the cinnamon sugar mixture. Bake for 20-25 minutes.
