Pre heat the oven at 130 deg C.
Beat the egg whites with an electric whisk till bubbles start to form.
Increase the speed and continue to whisk till it forms soft peaks.
Add the sugar, a tablespoon at a time and continue whisking at medium speed till all the sugar is added.
Continue to whisk at a high speed till stiff peaks form and all the sugar has dissolved. If you rub a little of the mixture between your thumb and forefinger, you should not feel the sugar.
Add the vinegar / lemon juice and vanilla extract and whisk till just combined.
Add the cornflour and fold in with a metal spoon till well incorporated.
Add four small blobs of the meringue to the four corners of a baking tray. Place a piece of parchment paper on top of the tray, pressing down on the meringue blobs. This helps to hold the paper in place while shaping.
Tip the meringue onto the centre of the parchment in a mound and spread out into a round of 9 inches in diameter. Shape it like a crater with the sides higher than the centre. This is to help hold the topping. You can put it in the oven at this stage for a rustic look. I wanted to pretty up mine, so used a spatula to smooth the sides and used a smaller spatula to make strokes all round. Each stroke was from the bottom to the top.
Place the tray in the centre of the pre heated oven and bake for 10 minutes.
Reduce the oven temperature to 100 deg C and bake for another 1 and a 1/2 hours.
Switch off the oven and let it cool completely inside the oven.
Don't worry if you see slight cracks on the outside of the meringue. It is quite normal and does not affect the texture of the meringue.