Preheat oven to 350°. Take out a nonstick 13-by-9-inch metal baking pan and set aside.
Cream butter and sugars with an electric mixer at high speed until fluffy. Add baking soda, cinnamon and salt, then mix at low speed to blend. Add eggs and vanilla extract and beat at medium until just incorporated. Add flour and mix on low speed until blended.
Scrape dough into pan, smoothing it in an even layer. Bake until lightly golden and set in center, about 30 minutes.
Transfer pan to a rack, and if desired, sprinkle cinnamon-sugar over warm bars, and then let cool completely. Or dust cooled bars with confectioners' sugar. Cut into 40 bars.