Preheat oven to 350°F (175°C). Line baking sheets with parchment paper.
Beat butter and both sugars for 2-3 minutes, until light and fluffy. Add egg, yolk and vanilla and mix at medium speed for another minute, scraping sides of bowl periodically.
Add cream of tartar, baking soda, salt and cinnamon and mix on medium-low speed to combine.
Add flour and mix on low speed just until thoroughly combined, scraping bottom and sides of bowl once.
In a small bowl, stir together the sugar and cinnamon for the cinnamon-sugar mixture.
Scoop out about two tablespoons of dough and roll into balls. As a reference point, my dough balls were the size of golf balls and weighed about 1.4 ounces (40 grams) each. Roll each cookie dough ball in the cinnamon-sugar and place two inches (5 cm) apart on parchment paper-lined baking sheets. Do not flatten. Sprinkle cookie balls with leftover cinnamon-sugar if desired.
Bake for 9-12 minutes, until cookies are puffy and cookie tops start to form cracks. Once they are puffed, baked for one additional minute then remove from oven. Allow to cool on baking sheets for 5 minutes before transferring cookies to wire racks to cool completely. Store cookies in airtight containers for up to one week. They also freeze very well.
*In Austria/Europe, use 2 teaspoons cream of tartar baking powder (Weinsteinbackpulver) and ½ teaspoon baking soda (Natron).