Make the Starter the Day Before Combine the starter ingredients in a medium-sized mixing bowl, cover, and allow them to rest overnight (roughly 12 hours).
The Next Day Make the Dough In the bowl of a stand mixer fitted with a dough hook, add the flour, sugar, salt and yeast and mix briefly. On Medium speed at the softened butter and mix until the butter is rubbed in lumps.
In a jug, whisk together the eggs, warm water, Fiori di Sicilia and the starter. Slowly add the wet into the dry until your dough comes together.
Knead on Medium High speed for about 4-5 minutes until the dough is smooth and shiny. This is a soft, sticky dough.
Cover the dough tightly with cling wrap and allow it to rise at room temperature for 1 1/2 - 2 hours, or until doubled in size.
Mix the raisins apricots, cranberries, candied peel, lemon and orange zest together in a bowl.
Gently deflate the dough, and on a floured surface knead in the fruit mix until well combined throughout.
Shape the dough into a ball and place it in a panettone pan or other straight-sided, tall 1 1/2 - 2-quart pan.
Cover the pan with cling wrap and let the dough rise again at room temperature until it's just crested over the rim of the pan, about 1 1/2 - 2 hours.
Once proofed egg wash the top of the panettone and bake the bread in a preheated oven at 400°F (200℃) for 10 minutes; reduce the oven heat to 375°F and bake an additional 10 minutes; then reduce the heat to 350°F and bake for 15 to 20 minutes, tenting with aluminum foil if the crust appears to be browning too quickly.
Panettone should sound hollow when tapped, Remove the panettone from the oven and cool completely.
Dust with powdered sugar to serve. Store at room temperature, well-wrapped, for up to a week or freeze for up to 4 weeks for longer storage.