Place the butter in a bowl, whisk in the sugar and salt. Add the eggs one at a time and continue to whisk until the mixture becomes lighter in colour. Mix in the flour, nuts, baking powder and cinnamon. Add the squash to the mixture. Place half of the dough in the prepared mould. Cover the rest of the dough and refrigerate.
Approx. 45 mins. in the lower half of an oven preheated to 180°C. Remove from the oven, allow to cool slightly, tip out onto a cooling rack and leave to cool completely. Wash the mould, grease and flour it. Transfer the refrigerated dough to the prepared mould. Bake, tip out and cool as above.
Trim the bases of the cakes so that they are level and place one on top of the other. Place the reserved squash stem on top of the Gugelhopf. Mix the icing sugar with lemon juice until smooth and drizzle over.