Line 9×13 pan with foil and give a light coating of cooking spray.
Sift the baking soda to remove any lumps.
Mix sugars and syrup in a medium-sized, heavy bottomed pan.
Stir while heating, use a candy thermometre to cook the mixture to 288F.
Remove pan from heat and quickly sprinkle baking soda over the mixture. Stir rapidly to thoroughly mix. It will turn bubbly and light colored.
Pour candy into lined pan, spreading only a tiny bit so as not to remove the air bubbles.
When candy is cool, smack with a heavy knife to break into pieces.
Cover in melted chocolate if desired.