Preheat the oven to 160C (320F). Line a baking tray with non-stick baking paper. Draw a circle of the size of the cake (usually 26cm diameter) on the baking paper. You will need three baking trays in total (or one large tray, depending on the size of the oven and cake).
Roughly chop the nuts in food processor. Place the nuts on a pan and roast for couple minutes. Remove nuts from the pan and cool them completely.
Transfer the egg whites to the bowl of an electric mixer (or large bowl if using a hand-held beater), and beat on low speed, until the eggs are foamy. Increase speed to high for 2-3 minutes or until soft peaks form.
Add the sugar, a third at a time, and continue to beat on high for 2-3 minutes. By this stage the mixture should be stiff and glossy.
Sift the flour; fold the flour and nuts into the meringue mixture.
Split the mixture in 3 even parts. Place each part in the middle of the circle drawn on the baking paper. Even out the edges with a spatula or butter knife.
Reduce the oven temperature to 120C (250F). Place the baking tray in the oven and bake meringue for 1 hour.
When all meringues have baked, place them back in the oven (still warm, but turned off) to dry out overnight or for 7-8 hours.