Place the butter in a bowl, add the jam, sugar, egg and salt, whisk together until the mixture becomes lighter in colour. Mix in the flour, mix to create a soft dough, do not knead, cover and chill for approx. 1 hr.
On a lightly floured surface, roll out the dough in batches to approx. 4 mm thick. Cut out animals using animal cutters, place on two baking trays lined with baking paper.
Approx. 15 mins. in the centre of an oven preheated to 160 °C (convection). Remove from the oven, allow to cool slightly, leave the biscuits to cool completely on a rack.
Spread the jam over half of the biscuits, top with the remaining biscuits.
Melt the cake icing in a bain-marie or in the microwave.Dip the animals in the cake icing, sprinkle with hundreds & thousands. Leave the biscuits to dry on a sheet of baking paper.