Pre-heat the oven to 190°C / 170°C fan assisted / gas mark 5 / 375°F.
Line a large baking sheet with baking parchment.
Stir the egg whites, sugar, vanilla together in a large bowl.
Fold in half the flour with the salt, then stir in the melted butter.
Fold in the second half of the flour then add a third of the flaked almonds so they are coated with the biscuit batter.
Rest the batter for 10 minutes.
Spoon one heaped tablespoon of batter onto the baking parchment and using the back of the spoon, swirl the batter into a thin circle so they reach about 9cm each. You are aiming for between 4-6 biscuits per batch. This will give you time to shape every biscuit after they are finished in the oven.
Repeat to create more circles of batter, evenly spaced apart by about 5cm. Sprinkle the rest of the flaked almonds over the top of each biscuit.
Bake for 6-8 minutes.
Remove from oven and whilst still hot, carefully life and shape over a rolling pin. Allow to set for at least 15 minutes then you can remove off the rolling pin to finish cooling.