Preheat your oven to 350 degrees Fahrenheit and prepare baking sheets by lining them with parchment paper. Set them aside.
Add the butter to a mixing bowl with the sugar and cream them together well using a hand mixer (or a stand mixer if you have one) until the mixture is light in colour. Be sure your butter is on the cooler side - if you use warm butter that's been sitting at room temperature for a long time your cookies will spread too much.
Add the eggs and mix well until combined, scraping down the sides of the bowl.
Add a sieve over the bowl and add the flour, cream of tartar, baking soda and salt into the sieve, using a spoon or your fingers to push the dry ingredients through the sieve to remove any lumps.
Mix the dry ingredients into the butter and egg mixture on medium speed until well combined.
Use a cookie scoop or a tablespoon to portion out the cookie dough by the tablespoon, rolling each piece of dough in your hands to form balls.
Combine the sugar and cinnamon for the coating and roll each of the balls of dough in the cinnamon sugar until they're completely coated.
Add them to your baking sheets, spacing the cookies out so they don't touch as they bake (these cookies spread quite a bit as they bake).
Bake at 350 degrees Fahrenheit for 10-11 minutes or until the cookies are golden brown and no longer soft in the middle.
Let the cookies cool on the baking sheet before enjoying so they keep their shape.