Place the butter in a bowl, add the sugar and salt, beat using the whisk attachment on a hand mixer. Add the eggs one at a time and continue to beat until the mixture becomes lighter in colour. Mix the flour with all the other ingredients up to and including the cardamom, stir into the mixture along with the squash and apple. Transfer the cake mixture to the prepared tin.
Approx. 75 mins. in the lower half of an oven preheated to 180°C. Remove from the oven, allow to cool slightly, remove the cake from the tin and leave to cool on a rack.
Whisk together the lemon juice and icing sugar. Spread the icing over the cake, sprinkle with the pumpkin seeds, leave to dry.