Preheat the oven to 400° F. Line baking sheet with parchment paper.

Melt butter in a small saucepan. Stirring constantly, continue to cook butter until brown specks start to appear at the bottom of the pan and the butter has turned a light amber color, giveing off a warm nutty/toffee scented aroma (about 3-5 minutes). Immediately remove from heat and pour into a medium heat proof bowl. Let cool

In a small bowl, whisk together flour, cream of tartar, baking soda and salt. Add the sugars to the butter and beat until light and fluffy. Beat in the egg and vanilla. Gently mix in flour mixture just until combine. Cover dough with plastic wrap and chill in the fridge or freezer until firm, about 10-15 minutes.

In a shallow bowl, combine the sugar and cinnamon for the coating. Roll dough into 8 balls. Roll balls in cinnamon sugar until well coated and place about 1-2 inches apart on prepared baking sheet.

Bake for about 8 minutes, until edges just start to turn golden brown but centers are still soft and puffy. Do not over bake. Cool on cookie sheet for 3 minutes and then transfer cookies to a wire rack. Store at room temperature in an air tight container.