Preheat the oven 350 degrees. Combine the warm water, yeast and 2 teaspoons sugar in a small bowl. Mix well and set aside to a warm place for about 10 minutes. (Note: if yeast mixture does not bubble, yeast is likely inactive) Combine the 4 cups of flour, 1/2 cup sugar, salt, nutmeg, lemon rind and add warm milk, melted butter, egg yolks and yeast mixture. Beat until smooth. Turn dough out on a lightly floured surface. Knead in enough remaining flour until the dough is no longer sticky. Continue kneading until the dough is smooth and elastic (about 10 minutes). Place the dough in a well-greased bowl. Turn once so greased surface is on top. Cover the dough and let rise in a warm place until doubled in bulk (about 1 1/2 hours).