Dissolve the sugar into the water in a heavy bottomed saucepan and let it bubble away over a medium heat.
The mixture should turn a golden caramel colour after around 5 minutes. DON’T stir the caramel mixture – the sugar will crystallise.
Once the caramel has reached the desired colour, take it off the heat and add the cream, butter and salt.
Stir until smooth, then pop the caramel mixture in the fridge to cool completely.
Once the salted caramel has cooled down, beat it with an electric beater until soft peaks form.
Use a small offset spatula or a knife, spread a generous amount of salted caramel on half of the brookies, and then sandwich them together with the remaining cookies.