In a small bowl, combine the warm milk and yeast. Let it sit for 5-10 minutes until it becomes frothy.
In a large mixing bowl, cream together the softened butter and sugar until light and fluffy.
Add the eggs one at a time, beating well after each addition. Stir in the vanilla extract.
In a separate bowl, whisk together 4 cups of flour and salt. Gradually add the flour mixture to the butter mixture, alternating with the yeast mixture. Mix until a soft dough forms.
Fold in the nuts, dried fruits, as well as the lemon and orange zest.
Knead the dough with an electric mixer or on a floured surface, working in enough of the remaining flour to form a soft dough. Continue kneading for about 10 minutes, or until it becomes smooth and elastic.
Place the dough in a greased bowl, cover it with a clean kitchen towel, and let it rise in a warm place for 2-3 hours, or until it doubles in size.
Punch down the risen dough and turn it out onto a floured surface.
Divide the dough in half. Shape each part of the dough into a ball and place it in a greased and floured panettone mold or a large, deep cake pan.
Cover the dough with a kitchen towel and let it rise for an additional 1-2 hours.
Preheat the oven to 350°F (180°C).
Bake the panettone for 45-50 minutes or until golden brown and a toothpick inserted into the center comes out clean.
Allow the panettone to cool in the pan for 10 minutes before transferring it to a wire rack to cool completely.
Once the panettone is completely cooled, dust the top with powdered sugar.
Slice and serve.