Place the egg whites, caster sugar, cornflour and lemon juice in a bowl. Beat the egg whites with an electric mixer until the meringue is firm and smooth. Fill a piping bag fitted with a plain tip with the meringue. Poach on a baking tray lined with baking paper.
Bake the meringue in an oven preheated to 95°C for around 2 hours. Turn the oven off and leave the meringue in the oven for a further 30 minutes.
Leave to cool, then use a rasp to file the tips a little so that the meringue is stable when turned out.
Melt some white chocolate with green colouring and dip 5mm to 1cm of the meringue into it.
Whip the cold cream with the mascarpone using an electric mixer. Gradually add the caster sugar. Fill two piping bags, one fitted with a plain tip and the other with a fluted tip, with the whipped cream.
Assembly
Turn the cold meringue over at the ends. Poach the whipped cream, alternating the piping bags.
Add cubes of kiwi fruit, apple sticks covered with lemon juice to prevent darkening, and fresh mint leaves and chill until ready to eat.