In a small bowl, mix together the flour, warm water, and yeast for the starter.
Cover and let it sit in a warm place for about 30 minutes, or until bubbly and foamy.
In a large mixing bowl, combine the flour, sugar, salt, and active dry yeast.
In a separate bowl, whisk together the eggs, warm milk, vanilla extract, and lemon zest.
Add the wet ingredients to the dry ingredients, along with the prepared starter.
Mix until a dough forms.
Turn the dough out onto a lightly floured surface and knead for about 10 minutes, or until smooth and elastic.
Gradually knead in the softened butter, a little at a time, until fully incorporated.
Place the dough in a greased bowl, cover with plastic wrap, and let it rise in a warm place for about 2 hours, or until doubled in size.
While the dough is rising, soak the mixed dried fruits in the rum or orange juice. If using nuts, add them to the fruit mixture.
Once the dough has risen, drain the soaked fruits and gently knead them into the dough until evenly distributed.
Shape the dough into a round loaf and place it in a greased and floured panettone mold or a high-sided round baking tin.
Cover and let it rise again for about 1 hour, or until it reaches the top of the mold.
Preheat your oven to 350°F (175°C).
Bake the panettone for about 35-40 minutes, or until golden brown and a skewer inserted into the center comes out clean. If the top browns too quickly, cover it loosely with aluminum foil.
Allow the panettone to cool completely in the mold before removing it.
Dust with powdered sugar if desired before slicing and serving.
Enjoy your meal!