Preheat the oven to 350°F (175°C). Whisk together the flour, cream of tartar, baking soda and salt; set aside. With an electric mixer, beat the butter and 1 1/2 cups sugar together until light and fluffy. Beat in the eggs one at a time. With the mixer on low, add the flour mixture, beating to combine.
In a shallow dish, combine the 1/4 cup sugar and the cinnamon. Form 1-inch balls (using about 1 tbsp of dough per cookie) and roll each in the cinnamon sugar before placing on ungreased cookie sheets about 3 inches apart (these cookies spread significantly!).
Bake 8 to 10 minutes, until the tops have crinkled and the edges are set but the centres are still soft. Let cool a few minutes on the baking sheet before transferring to wire racks to cool completely.
Notes
Cream of tartar is key: It gives snickerdoodles their signature tang and chewy, crinkly texture.Give them room: These spread a lot, so space them about 3 inches apart.Don't overbake: Pull them when the edges are set but the centres still look soft for chewy cookies.Recipe credit: Adapted from the Rogers Foods website.