Preheat oven to 375° F.
In a bowl, whisk together flour, cream of tartar, baking soda and salt until well blended. Set aside.
In a large mixing bowl or the bowl of a stand mixer, beat butter and sugar on medium-high speed until light and fluffy, 1 to 2 minutes.
Add molasses and beat until combined, scraping down the sides of the bowl as needed.
Add egg and vanilla and mix until smooth.
Add dry ingredients and mix on low speed until incorporated and no dry flour remains.
In a small dish, mix raw sugar together with cocoa powder and cinnamon until well blended.
Drop dough by the tablespoonful into sugar mixture, rolling until completely coated. (Dough will be sticky, but the sugar mixture should keep it from sticking to your hands.).
Arrange on non-stick or parchment-lined baking sheets, leaving 2 inches of space between cookies. Repeat with remaining dough.
Bake for 9 to 10 minutes or until cookies are just set on top and bottoms are lightly golden brown.
Let cool for 5 minutes on baking sheets and transfer to a wire rack to cool completely.