• In a food processor combine the flour, salt and lemon zest.
• Add the butter and the Ice water 1 tablespoon at a time, until dough pulls together.
• Roll the dough into a ball, press flat, cover with plastic wrap and chill for an hour.
• Roll out dough and transfer to a tart pan/flan dish.
• Place baking paper over the dough and fill the pan with baking beans/any beans.
• Bake for 25-30min.

For the Filling:

• Combine 750ml water, 230g sugar,salt, lemon juice and lemon zest in a saucepan and bring to a boil.
• Meanwhile, combine the remaining sugar,cornstarch, egg and remaining water until well incorporated.
• When the lemon mixture begins to boil, remove the saucepan from the heat and add the egg mixture a tiny bit at a time while whisking furiously (to ensure the egg doesn't become scrambled).
• Once all the egg is incorporated, return the saucepan to the heat and allow the mixture to boil until it becomes thick.
• Once thick, immediately remove from the heat and stir in the butter.
• Pour the filling over the cooled crust and allow the filling to cool and set.

For the Meringue:

• Whip the egg whites until soft peaks, then slowly add in the castor sugar.
• Continue to whip the mixture until stiff and shiny.
• Pipe (or simply spread) the meringue over the cooled filling.
• Bake the tart for 5min on 200ºC or use a blow torch to brown the meringue a little bit.