In a large bowl mix the fresh yeast, dried active yeast and 100g flour. Dissolve 100g sugar in 120ml warm milk and add to the bowl. Mix and let stand for about 10 minutes or until the mixture starts bubbling.
Dissolve the remaining sugar in the remaining warm milk; add to the yeast mixture along with eggs, egg yolks, oil, rum, vanilla and orange zest.
Add 700g of flour sifted with the salt, a little at a time, to create a soft dough. Add the melted butter and start kneading the dough on a working surface, stretching and folding the dough until it absorbs all the butter.
You will obtain a very sticky dough. Place dough back in the bowl, cover with cling film and let rise until doubled in size, about 3 to 4 hours.
Add the remaining 200g of flour to the dough, kneading it in until completely incorporated.
Grease and flour a deep mould or use a paper panettone case. Form the dough into a ball, tucking down the excess dough; place it in the mould or paper case. Cover and let rise in a warm place until it reaches the edge of the mould, about 3 to 4 hours.
Preheat the oven to 160 C / Gas 3.
Brush the top of the cake with egg white. Then, with scissors, make a the traditional Y cut on the top of the bread.
Bake in the preheated oven for about 1 hour. Check the centre of the bread with a skewer - if it doesn't come out clean, cover the top with foil and bake for another 15 minutes.
Remove bread from oven; set bread aside until cold before serving.