Make the biga: Combine all-purpose flour, instant yeast, and lukewarm water in a small bowl. Stir with a fork until a shaggy, rough dough forms. Cover tightly with plastic wrap and leave in a warm spot for 1 to 2 hours if making same-day, or 8 to 12 hours overnight in the refrigerator. The biga is ready when doubled in size and bubbly.
Prepare the aromatic mix and soak raisins: In a small bowl, combine honey, vanilla extract, orange zest, lemon zest, and finely chopped candied orange peel. Stir well, cover, and set aside. In a separate small bowl, place golden raisins and pour rum or warm water over them. Soak for at least 1 hour, then drain well and pat dry with a paper towel.
Make the first dough: Transfer the biga to your stand mixer fitted with the dough hook. Add lukewarm water and bread flour, mix on low for 2 minutes. Add egg yolks one at a time, waiting for each to incorporate. Add sugar in two additions, then add softened butter a few pieces at a time, mixing 10-12 minutes until smooth and shiny. Transfer to a buttered bowl, cover, and let rise until doubled, 2-3 hours.
Make the final dough: Return first dough to the mixer bowl. Add bread flour and mix on low for 2 minutes. Add remaining egg yolks one at a time, then sugar, salt, and the aromatic mix. Add softened butter piece by piece on medium-low, taking 12-15 minutes until smooth and glossy. On lowest speed, add drained raisins, chopped candied orange peel, and candied citron, mixing just until distributed.
First shaping and second rise: Lightly grease a clean work surface with softened butter. Turn the dough out and gently fold it into a smooth round ball, tucking the edges underneath. Place into your panettone paper mold. Cover loosely with plastic wrap and let rise until the dome is about 1 inch above the rim, 4-6 hours.
Score and bake: Toward the end of the rise, preheat your oven to 350°F (175°C), rack in the lower third. Once risen above the rim, uncover and let the surface dry for 15 minutes. Score a shallow cross into the top with a sharp knife, about 1/2 inch deep. Place the small cube of cold butter in the center of the cross.
Bake at 350°F for 40-50 minutes. Check after 25 minutes: if deeply golden, tent loosely with foil. The panettone is done when an instant-read thermometer inserted into the deepest part reads 94°C (201°F). The top should be a deep mahogany brown.
Cool upside down: Remove from the oven immediately and push two long wooden skewers through the base of the mold, crossing them to form an X. Flip the panettone upside down and hang it between two tall pots or books so it hangs freely. Let it cool completely upside down for at least 3 hours, preferably overnight. This prevents the delicate crumb from collapsing.
Once fully cooled, right it upright and remove the skewers. The panettone is now ready to serve or wrap.