Everyone's favourite baker Mary Berry gives you the lowdown on making the perfect royal icing.
- Sieve the icing sugar.
- Whisk the egg whites in a large bowl until they become frothy.
- Add the icing sugar to the egg whites, a spoonful at a time, and fold in.
- Add the lemon juice and glycerine and stir.
- Beat the icing until it is very stiff and white and stands up in peaks.
- Spread over the top and sides of the cake and rough up the icing with a spatula so that it forms peaks. (If you want a smooth icing you may need to thin the icing down a little with more egg white and use to ice the sides and top of the cake using a palette knife.)
- Transfer to a cake tin and seal up until ready for use.