In the bowl of a stand mixer fitted with the paddle (or a large mixing bowl and an electric mixer), combine the butter, sugars and whisk on medium-high speed until combined. well mixed, about 3 minutes.
Stop, scrape down sides of bowl and add egg, vanilla and beat on medium-high speed until well combined, light and fluffy, about 3 minutes.
Stop, scrape down sides of bowl and add flour, baking soda, cream of tartar, optional salt and beat on low speed until combined, about 1 minute.
Using a medium 2-inch cookie scoop or your hands, form about 14 same-sized piles of dough (2 heaping tablespoons each), roll into balls, and flatten slightly.
Place the mounds on a large plate or tray, cover with plastic wrap and refrigerate for at least 1 hour, up to 5 days. Do not bake with uncooled dough because cookies bake thinner, flatter, and more likely to spread.
Preheat oven to 350F, line baking sheet with Silpat or spray with cooking spray.
In a small bowl, combine the sugar, cinnamon and toss to combine.
Dredge each pile of dough with cinnamon and sugar.
Place mounds of dough on a baking sheet, spaced at least 2 inches apart (bake 8 cookies per sheet) and bake for about 9 minutes, or until edges have set and tops are finished, although they are slightly shallow cooked, pale and shiny in the center; do not overcook for soft cookies and pillows. For firmer cookies, bake an additional two to two minutes. Cookies reaffirm as they cool.
Let cookies cool on the baking sheet for about 10 minutes before serving. I let them cool on the baking sheet and don't use a wire rack.