Preheat oven to 150°C fan. Grease and line a 1-liter loaf tin.
Mix all dry ingredients for the sponge in one bowl.
In another bowl, whisk wet ingredients and add hot water last. Combine both until smooth.
Pour batter into tin and bake for 45 minutes (use less time for a gooey middle).
For the honeycomb: heat sugar and corn syrup/honey to 140-145°C or dark amber color.
Remove from heat, add bicarbonate of soda, stir gently, and pour into a lined tray. Let set without refrigerating.
Once honeycomb has hardened, blitz it and leave some chunks for crunch.
Whip mascarpone cheese, cream cheese, and vanilla together. Fold in honeycomb dust.
Once cake is cool, top with the honeycomb cream, slice, and serve.
