In a large bowl, dissolve yeast in warm milk.

Let stand until creamy, about 10 minutes. Add the egg yolk, butter and 2 cups of bread flour; stir well to combine.

Stir in the remaining flour, 1/2 cup at a time, beating well after each addition.

When the dough has pulled together, turn it out onto a lightly floured surface and knead until smooth and elastic, about 8 minutes.

Divide the dough into 3 equal pieces and roll each piece into a 14 inch long cylinder.

Braid the pieces together and place on a lightly greased baking sheet.

Cover with a damp cloth and let rise until doubled in size, about 1 hour.

Meanwhile, preheat oven to 425 degrees F (220 degrees C).

In a small bowl, beat together egg white and water.

Brush risen loaf with egg wash.

Bake in preheated oven for 20 to 25, until golden.