Warm the cream, milk, and half the sugar in a saucepan until steaming but not boiling.
Whisk the yolks with the remaining sugar. Slowly whisk in the hot dairy, then return everything to the saucepan.
Cook over medium-low heat, stirring constantly, until the custard reaches 170°F and coats a spoon. Stir in vanilla and salt, chill completely, then refrigerate for at least 4 hours.
Make the Honeycomb and Churn:
Cook the sugar and golden syrup in a clean saucepan over medium heat without stirring until deep amber, about 300°F.
Remove from the heat, quickly whisk in the baking soda, and pour onto the lined sheet. Do not spread. Cool completely, then break into small pieces.
Churn the cold custard according to the ice cream maker instructions. Fold in most of the honeycomb, transfer to a container, and freeze until firm.
Notes
Use a deep saucepan for honeycomb because the mixture expands dramatically.
Reserve a few honeycomb pieces in an airtight container for serving.