food colouring gels a mixture of colours,
Whisk together the egg whites and vanilla extract with an electric whisk until frothy. Sift over 300g of the icing sugar and whisk again until thickened and smooth.
Add the remaining icing sugar, sifting in a little at a time until you reach your desired level of thickness. If you’re using food colouring gels, divide the icing between bowls based on the number of colours. If you’re flooding biscuits, loosen with a few teaspoons of water first.