In a small bowl, combine the raisins with the rum and 2 tablespoons of hot water. Allow to soak at room temperature, stirring occasionally, until the raisins are plump and most of the liquid has been absorbed, at least 8 hours or overnight.
In a stand mixer fitted with a paddle attachment, mix together the flour, sugar, yeast, salt, lemon zest and vanilla bean on low speed until combined. In a medium bowl, whisk together the eggs, tepid water and honey. With the mixer on low speed, pour the egg mixture into the flour mixture. Increase the speed to medium-low and mix until all of the ingredients are combined. Add the softened butter, 1 tablespoon at a time, mixing until incorporated before adding more. Increase the speed to medium-high and beat until the dough is smooth and elastic, about 8 minutes.
Drain the raisins, discard the soaking liquid, and stir together with the candied citron and 1 tablespoon of melted butter. Stir this mixture into the dough with a wooden spoon.
Place the dough in a large bowl, cover with plastic wrap, and let rise in a cold oven with the door closed until it has nearly tripled in volume, 12 to 15 hours.
Locate and discard the vanilla bean, then sprinkle the dough lightly with flour and scrape out onto a lightly floured surface. Sprinkle a bit more flour onto the dough, then fold the edges of the dough in towards the center, forming a loose ball, and place, seam-side down, into the panettone mold. Cover with a damp kitchen towel (not terry cloth) and let rise in a draft-free place at warm room temperature until the dough is just above the top of the mold, 3 to 5 hours.
Preheat oven to 370 degrees F.
Place the dough-filled panettone mold on a baking sheet. Use a very sharp serrated knife to score an "X" across the entire surface of the dough. Place the 1 tablespoon chilled butter in the center of the X and bake until a wooden skewer inserted into the center comes out slightly moist but not wet, 60 to 75 minutes (the panettone will be very dark).
Remove from the oven and pierce 12-inch metal or wooden skewers all the way through the panettone (including the paper) 4 inches apart and 1 inch from the bottom so the skewers are parallel. Hang the panettone upside down over a large stockpot and cool completely before cutting. To store the panettone, wrap tightly in plastic wrap, then either place in a resealable plastic bag, or wrap again in foil. The bread will keep at room temperature for up to 1 week. (I have not tried freezing the bread, but I believe it would freeze well, wrapped in plastic, then foil, then placed in a resealable bag.)