Pre-heat oven to 160° celsius
Place icing sugar into a small bowl
Combine almond meal, pistachio meal, caster sugar, baking soda and vanilla extract in a large bowl
In a separate bowl, whisk the egg whites until soft peaks form
Fold egg whites into the rest of the mix, until smooth
Using a medium size ice cream scoop, roll tablespoons of mixture into balls, then toss them into the icing sugar, one at a time
Place the sugar-coated cookie balls onto a cookie tray lined with baking paper, leaving space for the cookies to spread slightly
Bake cookies at 160° for 15 minutes, until very lightly golden
Slide baking paper and cookies onto a cool surface for 10 minutes, before cooling completely on a rack.