Preheat the oven to 160ºC/325ºF/gas 3. Line two large baking trays with greaseproof paper.
Toast the nuts in a large frying pan over a medium heat for a few minutes, or until golden. Leave to cool, then roughly chop.
Sieve the icing sugar, cocoa powder and salt into a large bowl, then add the chopped nuts and vanilla paste. In another bowl, separate the egg whites (save the yolks for another day), then whisk for 3 to 5 minutes, or until soft peaks form. Fold the egg whites into the dry mixture until combined.
Scoop ½ a tablespoon of the mixture onto one of the prepared trays, then repeat with the remaining mixture, making sure you leave a rough 4cm gap between each spoonful (you may need to do this in batches if your trays aren’t big enough).
Place in the hot oven for 10 to 15 minutes, or until crisp on the outside, but still slightly gooey in the middle. Leave to cool for 5 minutes before transferring to a wire rack to cool completely.