Combine the butter and icing sugar and mix with a hand mixer. You don't need to whip it!

Add the egg whites and vanilla extract, then stir in the flour and salt.

Spread the mixture as thinly as possible on a silicone mat (Silikomart is my favorite).

Bake at 175C for 4-6 minutes or until it becomes golden brown.

Remove from the oven.

While hot, this think biscuit is quite elastic and it can be molded into a shape you like. If not, just let it cool down in the pan - as it cool, it becomes crispy.

Break into small pieces and preserve into an airtight container to keep it away from humidity.