Prepare the Baking Tin: Line a 22 cm square baking tin with greaseproof non-stick baking paper.
Heat the Ingredients: Place the caster sugar and honey or golden syrup into a saucepan with high sides. Heat over low heat until the sugar starts to dissolve.
Boil the Mixture: Once the sugar has dissolved, increase the heat. Continue whisking until the mixture reaches 140°C.
Add Bicarbonate of Soda: Quickly whisk the bicarbonate of soda into the mixture until well combined. Immediately pour the mixture into the prepared tin. Do not move or touch the mixture once it's in the pan, as this will knock the air out of it.
Cool the Honeycomb: Allow the honeycomb to cool completely in the tin.
Melt the Chocolate: Melt the dark chocolate in the microwave in short bursts until smooth. Use a fork to dip the honeycomb chunks into the chocolate.
Set and Store: Place the dipped honeycomb on a cooling rack to set the chocolate. Once set, break the honeycomb into chunks and store in an airtight container for up to 3 days.