Whisk together flours, starch, cream of tartar, xanthan gum, baking soda and salt until well combined, set aside.

In a stand mixer, cream together butter and 1 ½ cups sugar until smooth and fluffy. Add in eggs and vanilla extract, mix until well incorporated and smooth.

Slowly add dry mix to the mixer bowl, and carefully mix until well incorporated and smooth.

Wrap dough in plastic film, chill for 1 hour.

Preheat the oven to 375 F (190 C), line baking sheets with parchment paper.

In a small bowl, combine remaining sugar with the cinnamon, set aside.

Roll 1.25" balls out of the cookie dough, then roll in cinnamon sugar mix.

Arrange dough balls on baking sheets leaving at least 2.5" between cookies - they flatten out a fair amount.

Gently press the tops of each - flatten JUST enough to prevent the dough from rolling.

Bake for 9-11 minutes. Cookies will look puffy, but flatten out as they cool. Do not overbake!

Allow cookies to cool for 2 minutes before removing from baking sheets.

Cool completely before storing in an airtight container.