Lightly grease an 8 inch / 20cm cake pan (square or round then line it with parchment paper.
In a medium pot add the sugar and corn syrup and heat over low/medium heat stirring until the sugar dissolves, stop stirring and bring the mixture to a boil, insert a candy thermometer, do not stir, if necessary brush the sides of the pot with a pastry brush dipped in cold water to remove sugar crystals (I didn't find this necessary).
When the temperature reaches 280F (138C) (this will take a bit of time so do not increase the temperature), remove the pot from the heat and quickly stir in the baking soda (mixture will bubble, spit and increase in volume).
Pour the mixture quickly into the prepared pan, do not spread (bubbles could disappear). Let cool approximately 2 hours, then dip in chocolate if desired. Enjoy!
TO MAKE HONEYCOMB (SPONGE TOFFEE) BARK
Either by bain-marie or microwave melt the chocolate, chop the honey comb/ sponge toffee into small pieces and stir into the melted chocolate. Pour the mixture onto a parchment paper lined cookie sheet and let set in the fridge for 3-4 hours then break into pieces and serve.
Notes
Some people say the temperature should reach 280 - 284F but I find that the toffee tastes burnt if I go past 280F/138C.While this sponge candy treat is best fresh as honeycomb softens quickly, you can store it in an airtight container at room temperature away from humidity for up to a week. Chocolate coated honeycomb will stay fresh a bit longer. You can also prolong its life by adding it to other treats like ice cream!