Mix the yeast with the tepid water in a quart jar along with 2 tablespoons (30 ml) of the sugar. Let the mixture stand in a warm place for 10 minutes, or until it has nearly tripled its original bulk.

Scald the milk; add 8 tablespoons (120 ml) of the butter and stir until the butter has melted, then add the salt and the rest of the sugar. Transfer the milk-butter mixture to a large bowl. Stir in the lemon peel and the vanilla extract and let the mixture cool.

With a mixer or dough hook, beat in 2 cups (1/2 liter) of the flour. Beat in the yeast mixture. Beat in another 2 cups flour, the five whole eggs, one by one, and the white of the sixth egg. Beat until smooth.

If you are not using a dough hook, put aside the mixer and begin working the mixture with a wooden spoon, Add 3 more cups (3/4 liter) of the flour and mix until the resulting dough becomes unwieldy.

Scoop the dough out onto a floured work surface and add 1/2 cup (125 ml) of the flour. Knead with your hands, adding more flour until all the remaining flour is absorbed. The dough will now be soft, elastic, smooth, and still a bit sticky.

Place the dough in an oiled 3-qurt (3-liter) or larger bowl, and turn the dough until it is oiled all around. Cover the bowl with a dry dish towel, and place in a warm spot until it rises to nearly 3 times its original bulk ~- 3 to 4 hours.

When the dough has risen, punch it down and knead in the raisins and citron. Cut the dough into four equal parts.

Butter four casseroles or souffle dishes. Fix a collar of double-folded and buttered aluminum foil around the inside of each dish. Put a piece of dough in each pan, mark a cross in the center of the dough with a sharp knife and put the pans back in the warm spot. Cover all four dishes with a dish towel. Let the dough rise until more than doubled in size - a an hour or so.

Mix the yolk of the last egg wtih the sugar and water solution until smooth and brush the tops of the panettones wtih the mixture.

Bake in a preheated 400F (200 °C) oven for 10 minutes. Put 1/2 tablespoon (7 ml) of butter in the center of each cross, lower the heat to 375F (190 °C) and bake for 10 more minutes. Lower the heat to 350F (170 °C) and bake 30 minutes longer or until the panettones are crusty and golden brown on top and cake tester comes out clean.

Cool the cakes completely before removing from pans. Let stand for a day before cutting.