Mix the flour, sugar, salt and orange zest together in a large bowl.
Make a well in the centre, add the eggs and the melted butter; continue to mix until a dough is formed.
Dissolve the active yeast in warm milk.
Add yeast mixture into the dough and knead until well mixed.
Place dough in a lightly floured bowl, cover with a damp cloth and let it stand until it doubles in volume.
Spread dough out on a clean surface, then add the diced candied fruit, walnuts, almonds and pine nuts (reserve a few assorted nuts for decorating).
Knead until ingredients are well combined. Add the chocolate pieces and mix into dough.
Knead dough into a ball, dust with flour and make a hole in the center to form a doughnut-shaped cake.
Place on a floured baking sheet. Brush dough with the egg yolk and decorate with large pieces of candied fruit and extra nuts.
Cover cake with damp cloth and allow to rise for an additional 30 minutes.
Preheat oven to 350 degrees (180 C).
Bake cake in preheated oven for approximately 30 minutes, until it reaches a rich brown colour. Cover with foil if browning too quickly.
Allow to cool, dust with powdered sugar before serving.
