Divide custard evenly into 5 small ramekins. Level the top and place in the fridge.
Place water and sugar into a clean saucepan. Cook gently (do not stir) until a light toffee colour is reached. This should take approx 10–15 mins. Allow to cool slightly and carefully pour a thin layer of toffee onto the chilled custard. Serve immediately.
Alternate method for toffee topping: Sprinkle 1 tsp of caster sugar on top of each custard filled ramekin. Using a blowtorch, heat the sugar until it caramelises and forms a hard crust. Be careful not to burn the sugar as it can become bitter.