Preheat oven to 140C/ 275F/ GM1 and line a baking sheet with baking parchment
Weight the sugars into one bowl and stir to combine
Put the egg whites into a medium sized bowl and begin to whisk, using electric beaters, until just stiff
Add the sugar, 1 teaspoon at a time, whisking continuously, until all of the sugar has been added. This process will take around 5 minutes, but the meringue will be a much better texture than if you add it all in one go
Add the vinegar and cornflour and whisk for a further minute until fully incorporated
Finally, using a large metal spoon fold in the chopped hazelnuts
Spoon 6 heaps of meringue onto the baking sheet, leaving 5cm between each one. Gently press the back of a dessert spoon into the middle of each meringue, to make a slight indentation (or pipe neat nests if you feel like being fancy)
Put into the oven, turn the heat down to 120C/250F/ GM ½ and let cook for 30 minutes. After 30 minutes, turn the heat down to 100C/ 210F/ GM ¼ and cook for a further 30 minutes
Try to lift a meringue off the baking parchment - it should easily come away. If so, remove the meringues from the oven and let cool completely. If not, allow to cook for 5-10 more minutes and test again
Store in an airtight container until ready to use