Preheat oven to 375F degrees and line two cookie sheets with parchment paper. Set aside.
In a medium bowl, whisk together the flour, cream of tartar, baking soda, cinnamon, and salt.
2 1/2 cups all-purpose flour, 2 teaspoons cream of tartar, 1 teaspoon baking soda, 1 1/2 teaspoons cinnamon, 1/2 teaspoon salt
In the bowl of a stand mixer with the paddle attachment, or a large bowl with an electric mixer, cream butter and peanut butter on medium speed until smooth, 1 minute. Add the sugar and beat until light and fluffy, 2-3 minutes.
1/2 cup unsalted butter, 1/2 cup creamy peanut butter, 1 2/3 cups granulated sugar
Add the egg, egg yolk, and vanilla and beat until combined, 1-2 minutes.
1 large egg + 1 large egg yolk, 2 teaspoons vanilla extract
Mixing on low speed, slowly add the dry ingredients to the wet ingredients until combined.
Combine the cinnamon and sugar in a small bowl. Use a medium cookie scoop ( about 2 Tablespoons) to scoop the dough and roll it in a ball. Roll the dough ball in the cinnamon sugar and place on prepared baking sheets 2-3 inches apart.
1/4 cup granulated sugar, 3 teaspoons cinnamon
Bake cookies for 8-10 minutes, until the edges are set and tops crackle slightly. Cool on the baking sheet for 5 minutes then transfer to a cooling rack. Store in an airtight container at room temp for up to 5 days.