Melt 200g of chocolate and 100g of butter in a double boiler. Remove from the heat as soon as it melts and whisk vigorously to obtain a smooth preparation. Add an egg and mix quickly. Add 100g of icing sugar and mix quickly. Crumble dry biscuits (about 150g) into a large bowl. Add small pieces of marshmallow and/or pieces of dried fruit (almonds, hazelnuts, walnuts) and/or pieces of fruit paste to taste. (Note: the quantity depends on everyone's taste, but you shouldn't put too much either: if you only put marshmallow, you should count about ten cubes.) Pour the chocolate mixture into the bowl and mix well. Then pour it all on a sheet of cling film about thirty centimetres long. Fold the film to form a large sausage and place 6 hours in the refrigerator to harden it.