Beat the soft butter together with the sifted icing sugar and lemon zest until soft and fluffy (at least 5 minutes). Add the eggs one at a time, then add the salt and sifted flour.
Transfer the mixture into a piping bag, then shape the biscuits as desired. Decorate each biscuit with an Amarena Fabbri, then leave to rest for at least 30 minutes in the fridge.
Bake in a preheated oven at 180°C for 10-15 minutes, until lightly browned.