1/2 cup unsalted butter, softened 1/2 cup granulated sugar 1/3 cup light brown sugar, packed 1 large egg 1 teaspoon vanilla extract 1 1/2 cups all-purpose flour 1/2 teaspoon baking soda 1/4 teaspoon cream of tartar 1/4 teaspoon salt, optional and to taste For Rolling 1/4 cup granulated sugar 2 teaspoons cinnamon To the bowl of a stand mixer fitted with the paddle attachment (or large mixing bowl and electric mixer) combine the butter, sugars, and beat on medium-high speed until creamed and well combined, about 3 minutes. Stop, scrape down the sides of the bowl, and add the egg, vanilla, and beat on medium-high speed until well combined, light and fluffy, about 3 minutes. Stop, scrape down the sides of the bowl, and add the add the flour, baking soda, cream of tartar, optional salt, and beat on low speed until just combined, about 1 minute. Using a medium 2-inch cookie scoop or your hands, form approximately 14 equal-sized mounds of dough (2 heaping tablespoons each), roll into balls, and flatten slightly. Place mounds on a large plate or tray, cover with plasticwrap, and refrigerate for at least 1 hour, up to 5 days. Do not bake with unchilled dough because cookies will bake thinner, flatter, and be more prone to spreading. Preheat oven to 350F, line a baking sheet with a Silpat or spray with cooking spray. For Rolling – In a small bowl, combine sugar, cinnamon, and stir to combine. Dredge each mound of dough through cinnamon-sugar. Place dough mounds on baking sheet, spaced at least 2 inches apart (I bake 8 cookies per sheet) and bake for about 9 minutes, or until edges have set and tops are just set, even if slightly undercooked, pale, and glossy in the center; don’t overbake for soft, pillowy cookies. For firmer cookies, bake a minute or two longer. Cookies firm up as they cool. Allow cookies to cool on baking sheet for about 10 minutes before serving. I let them cool on the baking sheet and don’t use a rack. Cookies will keep airtight at room temperature for up to 1 week or in the freezer for up to 6 months. Alternatively, unbaked cookie dough can be stored in an airtight container in the refrigerator for up to 5 days, or in the freezer for up to 4 months, so consider baking only as many cookies as desired and save the remaining dough to be baked in the future when desired.