Here I have added the optional instructions to make your sugar cookies into chocolate cinnamon sugar cookies (my preferred flavour). I hope this all makes sense to you.
Add the vanilla and vinegar to the butter mixture and beat well
In separate bowl, mix the flour and baking soda (if making CHOCOLATE SUGAR COOKIES, Skip to STEP 7)
Gradually add the flour mixture and combine to make a soft dough.
Roll dough into 1" balls and roll in sugar to coat. Dip a glass in the sugar and flatten to 1/8th-1/4" (or use any other flattening method you choose). Repeat for the entire batch.
Bake at 350'F for 8-12 minutes, or until just beginning to be golden. Cool on pan for 2 minutes and then transfer to a rack. These will harden up as they cool.
Optional Instructions
Remove 2 tbsp of the flour
Add the cinnamon and cocoa to the flour mixture and add gradually to the butter mixture.