Aussie Key Lime Pie - cooking recipe

Ingredients

Crust
1 9-inch graham cracker crusts (or similar) or (200 g) packet digestive biscuits (in Australia I use Nice Biscuits)
120 g butter, melted
Filling
1 large lime rind, of finely grated
3 large limes, juice of
3 large egg yolks
1 (395 g) can sweetened condensed milk
Meringue Topping
3 large egg whites (optional)
175 g white sugar (caster sugar if available) (optional)
whipped cream (optional)

Preparation

If not using a prepared crust: Preheat oven to 180C (350F).
Process biscuits in a food processor then add melted butter.
Pulse several times until butter is well mixed with biscuit crumbs. (Alternatively, place biscuits into a plastic bag and crush with a rolling pin. Tip biscuit crumbs into a mixing bowl, then stir in melted butter.)
Place a loose based 23cm (9\") flan dish on an oven tray.
Tip crumb mixture into the flan tin.
Using your hands, press crumbs firmly into the base and sides of the tin.
Place flan tin (on its oven tray) onto the centre shelf of the oven and cook for 10-12 minutes until the crust is golden brown.
Meanwhile, in a small mixing bowl and using an electric mixer, beat together the egg yolks and the lime zest until the yolks thicken and the beaters leave a 'trail' in the mixture (about 2 minutes).
Now add the condensed milk.
Beat until mixture thickens and beaters leave a 'trail' in the mixture (about 4-5 minutes).
Add the lime juice and mix briefly to combine.
When the crust is ready, remove it from the oven and pour in the filling.
Reduce the oven temperature slightly to about 170C (325F).
Place the pie on the centre shelf of the oven and cook for 10-15 minutes being careful not to overcook it.
Remove pie (on its tray) from oven when the centre is JUST set.(This gives a smoother textured pie.)
Allow the pie to cool, then cover and chill in the refrigerator. (Note: If topping with meringue, simply cover the pie with plastic wrap and place in the refrigerator to chill. However, the plastic wrap tends to stick and ruin the smooth surface so, if not hiding this with a topping, cover it with an upturned dinner plate.)
Meringue Topping (optional): Reset (or preheat) oven to 150C (300F).
Grease two baking sheets/oven trays/cookie trays.
In a small mixing bowl beat egg whites until soft peaks form (make sure your beaters are scrupulously clean and dry).
Gradually add sugar, beating between each addition.
Beat until mixture is thick and glossy.
Spoon mixture into a piping bag fitted with a medium sized fluted piping tube.
Pipe small meringues, about 5cm (2\") high onto greased trays.(Alternatively, drop spoonfuls of the mixture onto the trays).
Place trays on centre shelves of oven and immediately reduce temperature to 140C (275F).
Cook for one hour (1 1/4 hours if you prefer a completely dry center), but do not remove meringues from oven.
Turn off heat and leave overnight (or at least until the oven is completely cool).
If not serving the pie immediately, store meringues at room temperature in an airtight jar or tin. They will keep well for several days.
When ready to serve the pie, spread a thin layer of whipped cream over the top and decorate with meringues.
(Serve extra meringues separately or store for later use).