In a mixing bowl, beat the egg whites until frothy, then gradually beat in half the icing sugar.
Add the lemon juice and glycerine and gradually beat in the remaining icing sugar, beating thoroughly after each addition to ensure a white icing, until the icing stands in soft peaks. Cover the bowl with a damp cloth or transfer to an airtight container and leave for 1-2 hours to allow any air bubbles to come to the surface.
You can flat-ice your cake or be creative using a palette knife. Or a combination of both! If using with marzipan underneath the icing, use leftover bits of marzipan to decorate the cake.
