Feed your levain with a ratio of 1:1:1.5, which the 1.5 parts is whole wheat flour.

While we're waiting for the levain to reach its peak, let's begin the autolyse.

Mix all the flour and milk powder together.

Add 122g of water, egg and honey into the flour mixture.

Roughly mix the dry flour with wet ingredients together until there is no visible dry flour left.

Cover with cling wrap and let it autolyse in the chiller until our levain reaches its peak.

When levain has doubled or tripled, add 40g of it, together with a bit of cold water to the dough.

Knead the dough for about 1 minutes.

Add salt and a little more of cold water into the dough.

(We're adding the 20g of cold water at this stage gradually. Depending on your flour's absorption capacity, you may not need all of it. If the dough feels fully hydrated, stop adding more water. If use all the cold water, the hydration of the dough will be 85%.)

Knead the dough until it reaches about 70% windowpane development. (For hand knead, best to use slap and fold technique that I showed before in shorts video.)

Then add in softened butter, and continue to knead until the dough has good extensibility, reaching 90% windowpane development.

Tidy up and round the dough using a scrapper, put it in a bowl, wrap and chill for 15 minutes.

After chilling the dough for 15 minutes, let it rest for another 15 minutes at room temperature.

Then, perform 3 sets of coil folds at 45-minute intervals.

If the dough is collapsing quickly after last set, perform one additional set of coil folds.

When the dough has grow into about double in size, it's ready to be shaped.

Lightly flour your work surface and the dough, then gently flip the bowl and turn the dough out onto the counter.

Dust another side of the dough with some flour again and flatten it out.

Fold it into thirds (1/3), like a letter, then let it rest for 10 minutes.

Gently roll out the dough with a rolling pin, not to degas it too much, until the width is almost the same as your loaf pan.

Roll the dough into a log and place it seam side down in a greased loaf pan.

Cover the loaf pan with its own cover or just wrap it tightly.

Place the dough in the refrigerator for overnight cold fermentation. Recommend not exceeding 12 hours.

Remove the dough from refrigerator and allow it to undergo final proofing at room temperature.

When the dough has filled up the loaf pan for about 60%-70% , preheat your oven to 200C, conventional mode (fan off).

Once the dough rises to 80% of the loaf pan, spray water on the surface and send it to the preheated oven.

Bake for 30 mins, rotate the pan half way through and cover loosely with aluminum foil if you're satisfied with the color.

When done baking, remove the loaf from the oven and knock the pan once to release excess steam.

Unmold immediately and let it cool completely on a rack.

Hooray! Sourdough shokupan unlocked!