The day before making this, prepare the sponge by mixing all of the ingredients together in a large bowl. Cover and place in the fridge overnight to rise.
The next day, remove the sponge from the fridge.
In the bowl of a stand mixer, combine the softened butter and honey.
Add the eggs and egg yolk, one at a time, then add the vanilla.
Add the sponge and mix to combine. Mix until it is mostly combined.
Add 2 cups of flour and the salt and combine. Cover and rest for 10 minutes.
Add the remaining flour, ½ cup at a time until it starts to pull away from the sides of the bowl. Knead until windowpane, about 8-12 minutes. The dough will be wet, but shouldn’t be too sticky.
Add the lemon and orange zest and dried fruits, and knead until well incorporated into the dough.
Cover the bowl and place in a warm place to rise for about 30-45 minutes. It does not have to be doubled in size, just somewhat risen.
Turn the dough out on a lightly oiled surface and equally divide it into 12 pieces. Shape into balls and place them into the panettone wrappers. Cover and allow to rise until puffy, about 30-45 minutes. Preheat the oven to 375 degrees F.
Once risen, brush the tops of the panettones with the egg wash and bake for 18-22 minutes, until golden brown and the internal temperature has reached 200 degrees F.