In a medium bowl, stir together the flour, baking soda, salt, and cinnamon. Add in the dry ingredients along with the chopped walnuts until no dry pockets remain. Let the batter rest for 20 minutes at room temperature. Then even divide the batter in your muffin tins, and sprinkle the tops with sugar. Bake for 15-20 minutes, or until a toothpick comes out clean. The tops should be lightly golden and puffed up.