Place butter into a microwave safe bowl. Heat for a few seconds, until about half of the butter is melted and half is still in softened "chunks".

Cream together softened butter and sugar. Add in egg and vanilla.

In a separate bowl, mix together flour, baking soda, and cream of tartar. Add dry ingredients to wet and bring together.

In a small bowl, combine the sugar and ground cinnamon for cinnamon-sugar mixture. (You can adjust this ratio to fit your taste).

Portion out dough with a cookie scoop (#40 size is perfect). Roll dough into balls and then roll in cinnamon sugar mixture before placing onto a parchment paper lined baking sheet.

Using the bottom of a glass that has been dipped in more cinnamon-sugar, press each ball into a flat cookie shape.

Bake at 350°F for 8-10 minutes. The cookies may look underbaked, but this timeframe is perfect for this size of cookie. Any longer and the cookies become hard after they have cooled.