Stir the ground almonds, powdered sugar and icing sugar in a bowl until well mixed.
Make a well in the center and add lemon juice and egg. Knead the mixture into soft, smooth, but firm dough.
Marzipan can be stored refrigerated, covered with cling film.
Makes 500 grams Marzipan is very versatile. You can mould it into shapes like fruits, roses, hearts etc, and serve as candy or use to decorate cakes.