Mix the yeast with the flour and as much water as necessary for the dough to be elastic. Wrap in a towel and put into a warm draft-free place (an unlit oven, for example) until doubled in size (it should take approx. 30 mins) and the surface is uneven. Make a small fontana with 4 tbs. flour. Crumble the dough cake on top of it, add 1/2 cup warm water and knead until the dough is elastic. Let rise in a warm place for 3 hours.
Punch down the dough, and then, knead in another 4 tbs. flour, with as much warm water as necessary. Place the dough in a warm place to rise for 2 hours. Combine the sugar, the whole egg and the yolks. Mix well and cook in a double boiler for a few minutes, beating the mixture with a whisk so that it becomes light and airy. Let cool.
Make another fontana with the remaining flour. Put in a pinch of salt, the risen dough, the butter and the egg mixture into the middle. Knead energetically for 20 mins. When the dough is smooth and elastic, add the raisins and candied peel. Grease and flour a sheet of waxed paper and place the dough in the center. Make a ring around it with a rectangular piece of cardboard and let rise in a warm place for at least 6 hours or until the dough has doubled in size.
Cut a cross on top of the cake with a sharp knife and put 1 tbs. butter in the middle. Cook the panettone in a pre-heated 400ºF oven for 40-45 mins. The cake is ready when a skewer inserted in the center comes out dry.
