How to Make It
In a small saucepan, melt the 1 1/2 sticks of butter in the milk over low heat. Pour the mixture into a medium bowl and let cool slightly, then whisk in the egg yolks. Whisk in the yeast and let stand until foamy, about 5 minutes.
In a large bowl, whisk the flour with the sugar and salt. Stir in the milk mixture until a very wet dough forms. In another large bowl, using a handheld electric mixer, beat the egg whites until stiff peaks form, about 2 minutes. Using a rubber spatula, fold the egg whites into the dough until incorporated. Scrape the dough into a very large greased bowl. Using your hands, shape the dough into a round loaf. Cover loosely with plastic wrap and let the dough rise in a warm place until doubled in bulk, about 2 hours.
Butter a 10-inch tube pan. Using your hands, punch the dough down and tear an opening in the center of the dough. Transfer the dough to the prepared pan, inserting the tube into the hole in the dough. Gently pat the dough to the sides of the pan. Cover loosely with plastic wrap and let rise in a warm place until nearly doubled in bulk, about 1 hour.
Preheat the oven to 325°. Bake the bread in the center of the oven for 25 minutes, until a crust is just starting to form. Increase the oven temperature to 375° and bake for 20 to 25 minutes longer, until the bread is golden and crusty. Let cool in the pan for 10 minutes. Remove the bread from the pan, cut into slices and serve warm.