Preheat the oven to 375°F and line two large baking sheets with parchment paper.

In a shallow dish, mix together 3 tablespoons of the sugar and the cinnamon. Set aside.

In the bowl of a stand mixer, cream together the butter and the remaining 1 1/4 cups sugar until light and fluffy. Add the egg and egg yolk and beat until creamy. Add the cream of tartar, baking soda, vanilla, and salt and mix until combined. Gradually add the flour and mix until just combined.

Use a 2-tablespoon cookie scoop to scoop the dough, then use your hands to roll it into balls. Roll the dough balls in the cinnamon sugar and arrange them on the prepared baking sheets, leaving at least 2 inches between balls.

Bake, one sheet at a time, for 8 to 9 minutes, or until the cookies are puffed. They will look underdone, but taking them out at this point helps them stay soft and chewy in the middle. Allow them to cool for 10 minutes on the baking sheet, then transfer to a wire rack to cool completely.