Preheat oven to 170°C
Use a non-stick spray to coat the inside of a 25cm x 5cm pie dish
Crush biscuits. Add butter and mix together. Tip into pie dish.
Spread crumbs onto base and up sides using the back of a tablespoon. Freeze for 10 - 15 minutes to firm.
Beat condensed milk, boiling water, lemon peel and juice, egg yolks and salt together until well combined
Carefully pour filling into crust to avoid disturbing the crumbs
Bake pie (without meringue) for 20 minutes.
Beat egg whites in a clean glass or stainless steel bowl until just beginning to foam
Add lemon juice and beat until mixture forms stiff peaks
Add castor sugar, a spoonful at a time, while beating fast
Sift icing sugar over in 3 batches and beat well (meringue mixture must be stiff and shiny and be able to hold its shape)
Remove pie from oven. Sift cornflour over filling (this acts as a ‘glue’ to hold the filling and meringue together).
Spoon meringue over hot filling, working it up and over the edge of the crust
Make a wave pattern in meringue by swirling it with a spatula. Return pie to oven.
Bake for another 35 minutes
Open oven door by 1cm, switch off oven and allow pie to cool inside