Instructions

• In the bowl of a stand mixer fitted with the paddle attachment, combine the egg, unsalted butter (1 stick), packed light brown sugar, and granulated sugar. Beat on medium-high speed until the mixture is well creamed, light and fluffy, about 5 minutes. (If using a hand mixer, beat for at least 7 minutes.)
• Add the Greek yogurt (or sour cream) and the vanilla extract. Beat on medium speed until incorporated and the mixture is fluffy again, about 2 minutes.
• Stop the mixer and scrape down the sides and bottom of the bowl with a spatula. Add the all-purpose flour, ground cinnamon, cornstarch, cream of tartar, baking soda, and the optional pinch of salt. Mix on low speed just until the dry ingredients are incorporated, about 1–2 minutes. Do not overmix.
• Add the cinnamon chips and fold them in by hand with a spatula, or pulse the mixer briefly (a few short bursts) just to distribute the chips evenly.
• Using a medium 2-inch cookie scoop, portion the dough into mounds and place them on a large plate or tray. Flatten each mound slightly with your palm or the back of a spoon.
• Cover the mounds tightly with plastic wrap (or transfer to an airtight container) and refrigerate for at least 2 hours and up to 5 days. Do not bake the cookies from warm dough, as warm dough will spread and produce thinner, flatter cookies.
• When ready to bake, remove the chilled dough from the refrigerator. If the dough was chilled overnight, you may let it sit at room temperature for about 15 minutes before baking (optional). Preheat your oven to 350°F (177°C).
• Line a baking sheet with a Silpat or parchment paper, or lightly spray with cooking spray. Place the chilled dough mounds on the prepared sheet at least 2 inches apart (about 8 cookies per standard sheet).
• Bake in the preheated oven for 8 to 9 minutes, or until the edges have set and the tops are just beginning to set (centers may still look pale and slightly glossy). If desired, rotate the baking sheet halfway through baking. Do not bake longer than 10 minutes, as the cookies will continue to firm up as they cool.
• Remove the baking sheet from the oven and let the cookies cool on the sheet for 5 minutes. Then transfer the cookies to a wire rack to finish cooling.
• Store cooled cookies airtight at room temperature for up to 1 week or in the freezer for up to 3 months. Unbaked, portioned dough can be stored airtight in the refrigerator for up to 5 days.