In a large mixing bowl, beat butter for about 30 seconds.
Add sugar, cocoa, soda and cinnamon. Beat until all is combined. Scrape the sides of the bowl.
Add egg whites and sour cream and beat again.
Beat in as much flour as you can with the mixer. Stir in any remaining flour. At this point you can cover the dough and refrigerate for about 3 hours, so it's easier to handle. I might have waited about 30 minutes ( impatient me, but how can you blame me - it's chocolate cookies we are talking about here! :) ).
Drop a teaspoon of the dough into powdered sugar and roll into a ball. Place on a greased or parchment paper lined baking sheet, 2 inches apart.
Bake for 8 to 10 minutes in a 350 degree oven. Edges of the cookies should be firm. Transfer all onto a wire rack and let cool.