In a pot, boil sugar and 80 g of water on high heat until it turns deep amber (about 5 minutes).
Quickly and carefully pour in the boiling water to stop the cooking. Stir until fully combined.
This will splatter — pour slowly and stand back!
In a large bowl, combine the condensed milk, melted butter, salt and honey.
Use an electric mixer and beat for about 2 minutes until emulsified.
Add the room-temperature eggs in batches, mixing after each addition.
Sift in cake flour and salt. Mix until smooth, then beat for another 2–3 minutes.
Dissolve baking soda in ½ tsp water and stir it into the batter.
Pour in the caramel water and mix until fully combined.
Strain the batter through a sieve into a parchment-lined square 8-inch baking pan.
Preheat oven to 180°C (356°F). Place a wire rack on the lowest rack of the oven.
Pour the rested batter into the pan and bake for 25-30 minutes until there is only the slightest jiggle in the center.
Let the cake cool completely before unmolding and slicing.
