Butter a 20cm square tin. Mix the sugar and golden syrup in a deep saucepan over a gentle heat until the sugar has melted. Try not to let the mixture bubble until the sugar has completely dissolved.
Turn up the heat a little and simmer until you have an amber coloured caramel (this won’t take long), then, as quickly as you can, turn off the heat, tip in the bicarb and beat with a wooden spoon until it’s disappeared and the mixture is foaming. Scrape into the tin immediately – be careful, the mixture will be very hot.
Leave the honeycomb in the tin for 1 hr-1 hr 30 mins until hard (it will continue to bubble).
Line a baking sheet with parchment paper. Melt the chocolate in a small heatproof bowl over a pan of just simmering water.
Snap the honeycomb into chunks and dip half of each piece into the chocolate. Drizzle with any remaining chocolate and a pinch of sea salt, if you like. Leave to set in the fridge for 1 hr.