Step 1

Preheat oven to 375°F (190°C). Line two large cookie sheets with parchment paper or silicone baking mats (always recommended for cookies). Set aside.

Step 2

Combine the granulated sugar and cinnamon together in a small bowl.

Step 3

Whisk the flour, cream of tartar, baking soda, cinnamon, and salt together in a medium bowl.

Step 4

In a large bowl using a hand mixer or stand mixer fitted with a paddle attachment, beat the butter and granulated sugar together on high speed until smooth and creamy, about 2 minutes. Add the egg, egg yolk, and vanilla extract. Beat on medium-high speed until combined. Scrape down the sides and up the bottom of the bowl with a rubber spatula as needed. With the mixer running on low speed, slowly add the dry ingredients to the wet ingredients in 3 different parts. The dough will be thick.

Step 5

Roll cookie dough into balls, about 1.5 Tablespoons of cookie dough each. I recommend this cookie scoop. Roll the dough balls in cinnamon-sugar topping. Sprinkle extra cinnamon-sugar on top if desired. Arrange 3 inches apart on the baking sheets.

Step 6

Bake cookies for 10 minutes. The cookies will be very puffy and soft. When they are still very warm, lightly press down on them with the back of a spoon or fork to help flatten them out. Allow cookies to cool on the baking sheet for 10 minutes and transfer to a wire rack to cool completely.

Step 7

Cookies remain soft & fresh for 7 days in an airtight container at room temperature.