Make the starter the night before you want to bake the panettone. Add your starter ingredients to the bowl of a stand mixer or a medium mixing bowl. Stir with a spoon to combine. Cover the bowl with plastic wrap and a towel and let it sit at room temperature overnight (8-12 hours).
Soak your raisins overnight at room temperature by adding them to a small bowl with the rum and covering them. See notes.
The next day, make your dough by adding your dough ingredients (not the raisins and zest yet) to the bowl with the starter. For the flour, start with 2 ½ cups and add the rest of your dough ingredients.
Using the paddle attachment of a stand mixer, mix the dough for about 30 seconds. Switch to the dough hook attachment and knead the dough for 15 minutes (I use speed 2 on my KitchenAid.) After a few minutes of kneading, if the dough isn't coming together, add ¼ cup of flour, scrape the bowl and hook, and knead some more. The dough will be sticky and won't completely clear the sides of the bowl. It's okay if there's still a 3-inch circle of dough sticking to the bottom of the bowl.
Add up to another ¼ cup of flour only if your dough still isn't coming together. (Adding too much flour will make your panettone dry, so just add enough so you can work with the dough.)
While your dough is kneading in your stand mixer, drain any excess rum from your raisins. Rinse and dry your orange and lemon. Zest the orange and lemon.
When your dough is finished kneading, add in your raisins and zest. Keep the dough hook but use the lowest setting to stir in the fruit until combined, about 1-2 minutes.
Gather the dough in a ball. You can leave it in the mixing bowl to rise or transfer it to a clean bowl, if you wish. Cover the bowl with plastic wrap and a towel and let the dough rise for 1 ½ hours in a draft-free spot (I like to set it in my microwave) until puffy.
Once the dough has risen, it's time to add it to your greased panettone pan (6 or 7-inches tall) or other straight-sided, tall 1 ½ quart-to-2-quart pan. You also could use a paper panettone mold.
Let the dough rise again in the pan or mold for another hour, covered with plastic and a towel.
Move your top oven rack down to a lower position to allow room for your panettone pan. Heat your oven to 400 degrees F.
While the oven is heating, beat one egg in a measuring cup or small bowl. Brush the egg wash onto your panettone dough. (You won't need all of the egg.)
When the oven is ready, bake your panettone for 10 minutes at 400. (Note, if you're using a panettone paper mold, you should only heat it to 390.)
After 10 minutes, reduce the temperature to 375 degrees F. Bake at 375 for 10 minutes.
Reduce the heat to 350 degrees F and bake the panettone for another 25-30 minutes. If your crust is browning too quickly, you can tent it with foil.
Remove the panettone from the oven and insert a cake tester or toothpick to make sure it's done. If using a paper mold, the panettone can stay in the mold. If using a pan, let the panettone rest for five minutes, then invert it onto a cooling rack. Turn the panettone right side up and let it cool completely before dusting it with confectioners sugar and slicing it.
The panettone is freshest on the first day. You can freeze the cooled panettone by wrapping it in plastic then placing it in a freezer bag (slice it first if you wish) to keep it fresh.
If you prefer to store leftover panettone at room temperature, wrap it tightly in plastic. (It helps to add a wedge of apple in there to keep it moist.) Then place the wrapped panettone in a sealed plastic bag. It should be eaten the next day or two before it gets too dry. Warming it a bit in the microwave helps to make it softer. You also can make French toast with the leftover panettone.
This recipe produces panettone that's a cross between pound cake and bread. It would take days of preparation to make the kind of panettone that's sold in stores. I much prefer this version anyway!Vanilla sugar is simply sugar stored in a container with split and scraped (empty) vanilla bean pods. When I have a recipe that calls for vanilla beans, I save the leftover pods and throw them in my sugar bowl for flavor. If you don't have vanilla sugar, you can add an extra ½ teaspoon of vanilla extract to the dough.Soaking the raisins in rum plumps them and imparts flavor and moisture to the panettone. For a non-alcoholic version, soak them in water. If you don't soak the raisins, they'll pull moisture away from the panettone and make it dry.Adapted in several ways from King Arthur Flour.