Make the candied lemon peel. Preheat the oven to 100°C.
Use a speed peeler to peel large strips of lemon zest from the lemon.
Combine the water and sugar over high heat stirring until the sugar has dissolved. Add in the lemon peel and simmer for about 10 minutes.
Drain the lemon peel, reserve the syrup and chill for later.
Lay the drained peel on a baking tray and bake in the low oven for about 30-40 minutes to dry out.
Remove the peel from the oven and roll in the additional caster sugar.
To make the Italian meringue, stir together the sugar and water over high heat until the sugar has dissolved and it begins to boil. Remove the spoon from the pan and leave boiling over high heat. Meanwhile, whisk the egg whites in a stand mixer or with an electric hand whisk until a cloud like texture.
Once the sugar syrup registers 121°C on a sugar thermometer, remove it from the heat and slowly pour into the egg whites whisking at high speed. Continue whisking until the mixture is cool, firm and glossy. Fill a piping bag with the meringue.
Make the Elderflower Lemonade: strain the lemon juice into a jug. Stir through the syrup and cordial.
Add one scoop of lemon sorbet into each glass. Fill each glass about ¼ of the way up with the elderflower lemonade. Top off each glass with tonic water.
Pipe the Italian meringue over the sorbet and brown with a blow torch. Finally, top the meringue with a piece of the candied lemon peel.