Mix together the sourdough starter, bread flour, and warm water in a clean jar. Cover it and let it sit in a warm area for about five hours until it doubles in size and bubbles up.

In a small heatproof bowl, combine 58 grams of bread flour with 58 grams of boiling water. Stir until it forms a thick, gelatinous paste and set aside to cool.

In a stand mixer with a dough hook, combine the levain, yudane, remaining bread flour, sugar, salt, milk, and eggs. Mix on low speed until shaggy, then increase to medium and mix for about five minutes.

Gradually add the room temperature butter in pieces while mixing. Continue mixing for another five minutes, until silky smooth.

Transfer the dough to a bowl, cover, and let rest in a warm area for about five hours until doubled in size.

Perform stretch and folds after the first hour of bulk fermentation by gently pulling and folding sections of the dough.

Refrigerate the dough for at least eight hours or up to 48 hours to enhance flavor and texture.

Remove the chilled dough, punch it down, and cut it into four equal pieces.

Roll each piece tightly into cylinders and place seam-side down in a greased loaf pan.

Cover the shaped dough and let it proof in a warm location for about five hours until it doubles again.

Preheat oven to 400ºF. Brush the proofed dough with an egg wash and lower the temperature to 350ºF. Bake for about 45 minutes until golden brown.