Parmesan would be a great alternative in this suggestion if allergic to nuts or nut intolerant.
Gently add the anchiovies and the sultanas, then increase the heat. Add one large level tsp of ground black pepper. Bring to the boil and simmer.
Continue occasionally stirring with a wooden spoon if possible the mixture. Reduce heat/ do not allow ingredients to boil over.
Because of the consistence of the butternut it will take a little longer for the potato slices to actually cook through.
Occasionally watch and continue to stir until they do.
When your soup has cooked and the potato slices are soft, add salt and pepper to suit your own taste.
Leave the star of anise in the pot.
Try crushing two walnuts and mix with some garlic salt (not too much) and sprinkle over the top.
If at a stage in a diet where cheese is ok for you, a sprinkling of parmesan could be excellent too as an alternative to /instead of walnuts.