Preheat the oven to 350°F (178°C).
Place the nuts on a rimmed baking sheet and spray them with water, sprinkle with a pinch or two of salt, and toast for 8 to 10 minutes. Transfer the nuts to a cutting board to cool and then coarsely chop them.
In a bowl, combine the 1 teaspoon salt, the flour, lemon and orange zests, candied orange and lemon peel, if using, fruit, nuts, rum, and vanilla.
In the bowl of an electric mixer fitted with a paddle attachment, beat the butter and sugar on medium speed for 2 minutes or until fluffy. Add the eggs and yolks and beat well.
Reduce the speed to low and add the flour mixture, mixing just until combined. Gradually add the starter and continue to beat on low speed until all the ingredients are incorporated. The dough should not be sticky or too firm. It should look buttery and a little ragged.
Turn the dough onto a lightly floured work surface and knead for 1 to 2 minutes, pushing the dough away from you with the heels of your hands and then folding it back over on itself. The dough will be smooth and satiny.
Transfer the dough to an oiled bowl, cover, and let rise in a warm place until doubled in size, at least 2 hours.
Gently turn the dough onto a work surface and divide it into 4 equal pieces if making smaller loaves or into 2 pieces if making larger loaves. Carefully handle the dough so as to keep as much air in it as possible. Let the pieces rest, covered with a clean towel, for 10 minutes.
To make smaller panettone, butter four 1-pound coffee cans or butter 4- to 5-inch-wide deep parchment paper molds (available online and at baking stores). To make larger panettone, butter two 2-pound coffee cans. Shape each portion of dough into a smooth ball and place it in a mold. Each mold should be about half full.
Beat the reserved egg whites and use the to brush the tops of the loaves. Cover and let the loaves rise until just slightly less than doubled, up to 1 hour.
Preheat the oven to 400°F (200°C). Adjust the oven rack to the middle position.
Uncover the panettone, place them in the oven, and reduce the heat to 350°F (175°C). Bake for 30 to 35 minutes is using smaller molds and up to 45 minutes for larger molds. The exact baking time will vary depending on the exact size of your cans or molds. The bread is done when a wooden skewer inserted into the center of the loaf comes out clean (between 190° and 195°F [87°C to 90°C] on an instant-read thermometer).
Cool the panettone in the molds for 15 minutes and then carefully remove the loaves from the molds or cans and place them on wire racks to cool completely.