Mary Berry's royal icing

Step 1

Sieve the icing sugar.

Step 2

Whisk the egg whites in a large bowl until they become frothy.

Step 3

Add the icing sugar to the egg whites, a spoonful at a time, and fold in.

Step 4

Add the lemon juice and glycerine and stir.

Step 5

Beat the icing until it is very stiff and white and stands up in peaks.

Step 6

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.)

Step 7

Transfer to a cake tin and seal up until ready for use.