Preheat the oven to 180 C / fan 160 C / Gas Mark 4. Line two baking trays with baking paper. Fit a large, round (1A) nozzle to a piping bag ready for the mix.

Add half the granulated sugar to the egg whites and using an electric whisk to beat until you have soft, glossy peaks. You should be able to turn the bowl upside down and nothing moves! Set to one side.

Add the rest of the sugar to the egg yolks and beat with an electric whisk until the mix pales and goes fluffy - it should increase in size.

Add a small amount of the egg white to the egg yolk mixture and fold in with a metal spoon, to loosen the mixture. Add the rest of the egg whites and fold gently until almost combined.

Mix the gluten free flour, xanthan gum and baking powder in a bowl and then sift into the egg mixture. Fold in carefully until there are no streaks of flour - make sure you're folding not beating the mixture. You want to retain as much air in it as possible!

Spoon the mixture into the piping bag and then pipe the mixture onto the baking sheets into thick lines, approximately 3.5 inches long. Make sure they're all around half-an-inch apart so they don't spread into each other.

Dust the fingers liberally with icing sugar (don't worry about excess on the tray!) and then bake for 15-18 minutes until slightly golden round the edges and crackled.

Remove from the oven and cool on a rack before eating. Keep in an airtight container for up to 3 days or freeze.