Mix the levain ingredients in a jar or straight-walled container with space for at least 300% growth.

Press the starter down with your knuckles or a spatula to create a uniform surface and to push out air.

Let the levain ripen and rise. At a temperature of 76-78°F, it typically takes up to 10-12 hours for this sweet stiff levain to peak.

In a sauce pan set to medium heat, stir the milk and flour from the tangzhong ingredient list until blended. Cook for several minutes until it thickens.

In the bowl of a stand mixer, add the milk, egg, tangzhong, salt, sugar, diastatic malt powder and levain.

Mix with a spatula for a few seconds and also break up the levain into many smaller pieces. Next add the flour and vital wheat gluten.

Allow the flour to hydrate (fermentolyse) for 20-30 minutes.

Mix on low speed and then medium speed until you see moderate gluten development, which may take 5-10 mins.

Lower the mixer speed to avoid splashing, and then drizzle in the melted butter a little at a time.

Once all the butter has been incorporated, increase the mixer speed gradually to medium. Mix at medium until the gluten is well developed, approximately 10 mins.

On the counter, shape the dough into a tight ball. Place it in a bowl, cover and ferment for 2.5 to 3.5 hours at 82°F.

Prepare your pan by greasing it or lining it with parchment paper.

Lightly flour the top of the dough. Scrape the dough out onto a clean work surface and divide it into four pieces.

Shape the pieces into tight balls and allow them to rest for 5 minutes.

Using a rolling pin, roll out each ball into a square and then letter fold it.

Arrange the rolls of dough inside your lined pan, alternating the direction of the swirls.

Cover and let the dough proof for 6-8 hours at a warm temperature.

Brush the dough with the egg-milk wash and begin preheating the oven to 350°F.

Bake the loaf for 50 minutes or until the internal temperature is at least 190°F.

After 50 minutes, lower the oven temperature to 325°F and remove the bread from the pan. Bake an additional 10 minutes.

Let the bread cool about two hours before slicing.