Add the flour, cornstarch, baking powder, and salt to a small mixing bowl (3-4 cups) and whisk to combine. Set it aside.

Using either a stand mixer fitted with a paddle attachment, or a medium-sized mixing bowl (2-3 quarts) and a handheld mixer, on medium-high speed, beat together the softened butter and cream cheese for 1½-2 minutes until light and well combined.

Lower the mixer speed to medium-low. Add the granulated sugar and continue mixing for another 1½-2 minutes or until smooth.

Add the egg and vanilla, mixing well until no yellow or brown streaks remain.

Add the flour mixture ½ cup at a time, mixing just until incorporated. Cover the mixing bowl with plastic wrap and chill in the refrigerator for 1 hour.

Preheat the oven to 375°F. Line a baking sheet with parchment paper.

Add the ⅓ cup of granulated sugar and ground cinnamon to a shallow bowl and stir to combine.

Remove the mixing bowl from the refrigerator. Scoop 1 tablespoon of the cookie dough. Roll into a ball. Roll the ball in the cinnamon sugar. Place on the baking sheet, 2 inches apart. Repeat.

Bake for 8-9 minutes. (Remember, all ovens cook differently, so keep a close eye on the cookies beginning at the 7-minute mark.) Since the cookies are coated in cinnamon, it will be hard to see if the cookie edges are golden. Remove the baking sheet from the oven and carefully use a spatula to look at the underside of the cookie. It should be a light golden brown. Do not overbake the cookies. They will go from tender and creamy to dry very quickly. Allow the cookies to rest on the baking sheet for 2-3 minutes before transferring to a cooling rack to cool completely.