Line a loaf tin or a Christmas pudding container with cling film.
In a large bowl, mix the vanilla ice cream with the Christmas pudding and chopped nuts.
Pour the mix into the prepared tin and place in the freezer overnight.
To serve, lift and unwrap the semifreddo out of the mold and turn onto a platter. For extra decadence, you can pour melted chocolate over it, and garnish with berries, chopped pistachios and icing sugar.