Whisk the egg whites until lightly whipped. Add the icing sugar a few tbsps at a time, whisking continuously until all incorporated. Add the glucose and lemon juice.

Continue whisking until the icing is thick enough to hold stiff peaks when you lift the beaters and is smooth and shiny.

Use a palette knife to spread the icing over the top and sides of your marzipaned cake. For a snowy effect, make little dips and peaks with a teaspoon. Leave to firm up somewhere cool and dry (not the fridge) for 24 hrs before cutting the cake.