In the bowl of a stand mixer fitted with the paddle attachment or a large mixing bowl with an electric hand mixer, beat the butter until soft shiny and light in color.
Add the sugar until light and fluffy. Add the egg and vanilla, combining until fully mixed. Set aside.
In a separate bowl, sift together the flour, cream of tartar, cinnamon, salt, baking soda and nutmeg.
In 3 batches, combine the dry ingredients to the wet ingredients.
Turn the cookie dough into a piece of plastic wrap and chill for 1 hour, but up to 24 hours. Using plastic wrap ensures the dough won't dry out.
In a small bowl, combine the sugar and cinnamon for rolling.
Preheat the oven to 375°F and line a baking sheet with parchment paper.
Scoop out 1 1/2 tablespoon scoops of dough, roll in cinnamon sugar mixture and then place 2 inches apart on a cookie sheet. Press each ball lightly with a glass until 1/2 inch thick.
Bake for 10 minutes, or until just cracking. You should be able to see shiny dough inside the cracks, which means the cookies are done.
Allow to cool for 2-3 minutes on the cookie sheet and then carefully transfer to a cooling rack.
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Notes
If you use salted butter, omit the additional fine sea salt.