In a bowl combine flour, salt, baking soda and cream of tartar. Mix well and set aside.
In a large mixing bowl cream butter and brown sugar with a mixer. Add egg and vanilla and continue beating until smooth. Gradually fold the dry ingredients into the mixture, using a wooden spoon. Make a soft dough and let it cool in the fridge for 15-30 minutes.
Line two large baking tins with parchment paper. Preheat oven to 360 degrees F/180 degrees C.
In a small bowl combine sugar and cinnamon and stir to blend.
Make small balls out of the dough and coat them well with cinnamon sugar. Arrange them on top of the baking sheets, not too close one next to another.
Bake for 10-12 minutes or until the bottoms start becoming slightly golden brown around the edges.