In a mixer, whip 1 litre of cream with the sachet of semifreddo mix. when the desired consistency is reached, divide the mixture into two halves. Add the pistachio cream to one half and the nougat cream to the other. Use a piping bag to put 50g of nougat semifeddo into a small mould, followed by the same amount of pistachio semifreddo. Freeze the semifreddi for at least 4 hours. Put the remaining 300ml of cream into a small pan and bring to the boil, then remove from the heat and add the chocolate broken into pieces. Mix well until the chocolate is completely melted. Pour sauce onto the centre of a dish, arrange the semifreddo on top and garnish to taste before serving.