In a large mixing bowl, beat together butter and sugar until fluffy. Then add eggs, milk and vanilla and beat until creamy.
In a different medium bowl, whisk together flour, cream of tartar, baking soda and salt.
Gradually add dry ingredients to butter mixture and beat until creamy.
Cover and chill dough for at least 30 minutes for best results.
Preheat oven to 350 degrees F.
Combine sugar and cinnamon in a small bowl while oven is preheating.
Line baking sheets with parchment paper or silicone mat.
Place on prepared baking sheet and bake for 9-11 minutes.
Remove from oven and let cool for 2 minutes on baking sheet and then place onto wire rack to cool.
Store in airtight container.