Preheat the oven to 200 C / 180 C fan / Gas 6. Line or grease 2 large baking trays.
Process the almonds and icing sugar in a blender till fine, then sieve in the cocoa powder. If you don't mind a chewier biscuit you can also skip the blending and place the ground almonds straight into a bowl.
Whisk the egg whites with an electric whisk until soft peaks, then add the sugar. Whisk until a slight stiff peak forms.
Next add half of the chocolate powder mix into the egg whites and fold in gently. Then fold the rest in.
Now it may seem odd but next you need to stir the mixture until it becomes a gloopy consistency, until it comes off the spoon like lava. The mixture may seem runny but it doesn't matter as it means the biscuits will be light.
Then pipe the mixture onto the baking trays leaving at least 1 to 2 cm gap in between each. It doesn't matter what shapes and sizes they are.
Leave at room temperature on the tray to dry out for 30 minutes. Then drop the trays on the work surface a few times to release any air bubbles.
Bake for 10 minutes. Remove from the oven and leave for further 5 minutes on the baking tray, then remove and cool.