Whisk together the sugar and cornflour in a wide saucepan. Stir in the water and orange juice then bring to a boil over medium-high heat whisking until thickened.
Stir in the cherries and orange zest then return to a boil. Reduce heat and simmer for 10 minutes.
While the cherries are cooking spoon the ice cream into serving bowls.
Remove the cherries from the heat and stir in the cherry essence.
Pour in the brandy and ignite with a long lighter. Gently shake the saucepan until the blue flame has extinguished itself.
Spoon the cherries over the bowls of ice cream.
The flames may get quite high when flambéing so pay attention to anything flammable above and around where you ignite the cherries. When the initial large flame has died down a small blue flame will continue to burn for several seconds. Shake or stir the cherries gently to expose more alcohol to the flame being careful that they do not burn. The goal is to have the small blue flame burn for as long as possible thereby reducing the raw alcohol flavour, caramelizing the sugars and entertaining your guests.