Bring to a boil the butter, brown sugar and syrup. Boil about 2 minutes. Remove from heat and add vanilla and baking soda. Stir quickly as soda makes it foam.
Pour over cereal mixture and mix well. Bake 225* for 1 hour, stirring every 15 minutes. Spread out on foil,(I use freezer paper because it is bigger) break apart and let cool. Enjoy!