1. In a large bowl (mixer) mix together warm water and yeast until dissolved. Let mixture ferment for 10 minutes.
2. Add milk, sugar, butter, lemon zest, vanilla, whole eggs, and egg yolks. Beat on low speed to blend. Then beat on medium for 3 minutes.
3. Add 4 cups of the all-purpose flour and salt to the mix and beat on medium speed. Gradually add more flour bit by bit, while mixing, until soft dough is formed (may not use all of the flour).
4. Turn the dough out onto a floured surface and knead it until smooth and elastic (8-10 min)
5. Place dough in an oiled bowl. Cover and let it rise until doubled in bulk (~1 hr)
6. Preheat oven to 375º F
7. Punch the dough down and knead until smooth (several minutes).
8. Place dough in greased Colomba pan (can be found at www.fantes.com)
9. Cover the bread with a sheet of buttered wax paper and a towel. Let the bread rise in a warm place until almost doubled (~20 min). *Be careful not to let it overrise*
10. Gently brush the bread all over with the egg white and sprinkle the wing tips and tail section with brown sugar.
11. Bake until bread is golden brown (~50 min). Carefully transfer bread to a rack to cool.