For the baked Alaska, place the water and sugar into a pan and bring to the boil.Skim the surface and wipe the sides of the pan with a wet pastry brush to remove any sugar crystals, and then increase the heat so that the syrup boils rapidly. Insert a sugar thermometer. When the sugar mixture reaches 110C/225F beat the egg whites with an electric mixer until stiff peaks are formed.When the sugar mixture reaches 121C/250F remove from the heat. It will have formed syrup.
Turn the electric mixer onto the lowest setting then pour the sugar syrup into the egg whites in a thin, steady stream, continuing to beat until all the syrup is incorporated.Continue to beat at a slow speed until the mixture is almost cold, this can take up to 15 minutes.
Place the crushed biscuits onto a square off grease proof paper and top with a scope of ice cream.Pipe the meringue around the ice cream, covering completely from top to bottom.Store in the freezer.
To Serve: Glaze the meringue with a mini-blowtorch, or bake briefly in a very hot oven.