Preheat oven to 160 C / 320 F fan force.
In a bowl, add the egg whites, salt, vanilla, lemon juice and zest. Combine with a whisk.
Sift in the flour and icing sugar into the bowl. Add the melted butter and whisk gently until no lumps. (Do not whip the egg whites)
Add the almonds and fold in using a spatula.
Pour the mixture on a baking tray lined with baking paper. Spread it out thin with a spatula. (My baking tray is approx 45 cm x 35 cm or 18 in x 14 in)
Put the tray on the middle rack of a preheated oven at 160 C / 320 F fan force for roughly 20 minutes.
After 20 minutes, take the tray out. Cut with a knife or break off the edges of biscuit that are really brown and put them on the rack to cool. These pieces will not require further cooking.
Cut / break up the rest of the biscuit into smaller pieces and grill them at 160 C / 320 F for 10 - 15 minutes or until golden. Remember to WATCH THEM!!! (Note 1)
Take the biscuits out and let them cool on a rack.