Instructions

1. 1
   Preheat oven to 375°F (190°C or Gas Mark 5)
2. 2
   In a medium mixing bowl, beat butter with an electric mixer on medium to high speed for 30 seconds.
3. 3
   Add the 1 cup sugar, baking soda, cream of tartar, and vinegar. Beat until combined, scraping sides of bowl occasionally.
4. 4
   Beat in egg and vanilla until combined.
5. 5
   Beat in as much of the flour as you can with the mixer. Stir in any remaining flour.
6. 6
   Cover and chill dough for 1–2 hours or until easy to handle.
7. 7
   Combine the 2 tbsp sugar and the cinnamon in a small bowl.
8. 8
   Shape dough into 1-inch (2.5 cm) balls. Roll balls in cinnamon-sugar to coat. Place balls 2 inches (5 cm) apart on an ungreased cookie sheet.
9. 9
   Bake for 10–11 minutes or until edges are golden. Transfer to a wire rack and let cool.