The night before: In a bowl, combine starter ingredients, cover with plastic wrap, and set aside to rise overnight. In another bowl, combine raisins, peel, and rum. Cover and allow to marinate overnight. Drain and reserve rum for other use.
The next day: In a mixer, whisk together eggs, sugar, orange zest, and vanilla. Once well mixed, whisk in the starter mixture.
Using a paddle attachment, gradually add flour and salt into the mixture. Once combined, add softened butter and continue kneading for another 5 minutes. Add the marinated fruit and continue kneading for just a few seconds until incorporated.
Lightly flour a clean surface and dump out the dough. Sprinkle to top with a light dusting of flour and gently knead until a smooth, slightly sticky dough forms. Transfer to a large oiled bowl, lightly spread oil over the surface of the dough, cover, and allow to rise for several hours or until more than doubled in size.
Once risen, gently punch down the dough and divide into 10-12 equal portions. Place in small panettone or cake molds set on baking trays lined with non-stick spray. Set aside and allow to rise for 30 minutes or until doubled.
Preheat oven to 350°F. Brush egg wash over the surfaces. Bake for 15-20 minutes or until the top is golden brown. Allow to cool completely.