Place the four Ferrero Rocher chocolates in the freezer until nice and hard.
Heat the oven to 140ºC (285ºF). Line a large flat baking tray with greaseproof paper and draw two identical circles of around 18cm each.
In a large bowl (or using a food processor) whisk the eggs until stiff peaks form.
While the meringues are mixing, blitz up the four frozen Ferrero Rocher chocolates in a blender until they are crumbs. Set to one side.
Slowly add the sugar to the eggs, one tablespoon at a time. Allow time for each tablespoon to become fully incorporated (dissolved) before adding the next one. When all of the sugar has been added, your eggs should be beautifully glossy.
Add the cornflour and white wine vinegar and continue to whisk just for a short while (until everything is incorporated).
Finally, very gently fold in the Ferrero Rocher, just until it is mixed in (be careful not to knock all of the air out of the eggs).
Divide the mixture equally between the two circles on your prepared tray smoothing out to the edges of the circles, making them as equals and level as possible (so that they will bake evenly).
Bake for 50 minutes then turn the oven off. Leave the meringues inside until they are completely cold (if you can, overnight is best).