Preheat the oven to 180 degrees Celsius. In your food processor, combine the ingredients for the pastry, and pulse until they form a ball. If the mixture is particularly sticky, wrap it in some cling film and refrigerate for about half an hour, to firm it up. Once it’s firmed up, press the dough into a greased fluted tart tin, and poke lots of fork holes in the bottom, to allow the air to escape while it cooks. Place in the oven for 10 minutes.
In a large saucepan, combine all the ingredients for the tart filling, and turn to a medium heat. Allow to cook for around 15-20 minutes, stirring intermittently, until the apple pieces are soft and the orange juice liquid has become a syrup. Remove from the heat.
Once the pastry has cooked, fill the tart with the apple mixture, and return to the oven for 10-20 minutes.
While the tart is cooking, beat the egg whites in a clean bowl until stiff peaks form. Add the caster sugar, vanilla bean paste and nutmeg, and continue to beat until well combined, glossy and free of any sugar related grit.
Allow the pastry to cool a little, and then gently spread the meringue atop the tart. I used a blow torch to gently cook the top of my meringue, but if you don’t have one, you can return the tart to the oven for 10-15 minutes, on a lowered heat of 160 degrees Celsius. Serve while warm.