Overnight Soft Sourdough Milk Bread (Shokupan)

Directions

1. Build Levain (12pm): Combine 50g sourdough starter, 60g bread flour, 60g water, and 25g sugar in a jar. Leave it in a warm place to rise until doubled (~6-8hrs at 22C). You may find it helpful to place a rubber band around the jar to measure when the levain has doubled in volume.
2. Make Yudane (12pm): Carefully combine 60g boiling water and 60g bread flour in a heat-safe bowl and whisk until all the flour is hydrated and the mixture forms a thick paste. Cover with a clean towel or plastic wrap and let cool for a few hours until it's time to build the final dough.
3. Final Dough - Autolyse (6pm): Mix together all final dough ingredients *except* for salt and butter until all the flour is hydrated. Cover and leave for 30 minutes. Note: You'll only use 170g of your levain - keep the remaining amount for your starter!
4. Final Dough - Mix Pt. 1 (6:30pm): Add salt to the dough and knead until the dough feels smooth and elastic, about 5 minutes by hand or 3 minutes on low in a stand mixer.
5. Final Dough - Mix Pt. 2 (6:40pm): Add butter to the dough bit by bit, mixing in between and ensuring the butter is fully incorporated before adding more. Continue to knead until the dough reaches the windowpane stage, meaning the dough can be stretched until it's translucent without ripping. This can take ~10-15min in a stand mixer on low-medium speed. The dough should be smooth, shiny, and stretchy.
6. Final Dough - Bulk Ferment (7pm): Transfer to a clean and lightly oiled bowl, cover, and let rise at room temp (for me, ~22C) for 2 hours. The dough should have risen somewhat but not doubled.
7. Final Dough - Pre-Shape (9pm): Transfer dough onto a lightly floured surface. Divide dough into 2 or 3 equal parts and shape each into a ball and rest for 30 minutes, covered by lightly greased plastic wrap.
8. Final Dough - Shape (9:30pm): Lightly flour your surface and a rolling pin. Now it's time to shape: De-gas each ball by pressing down with your hand, then using your rolling pin to roll it into an oval ~1cm thick. Then, starting from the short side of the oval, tightly roll up the dough (like a jelly roll) and place into a lightly oiled loaf pan seam side down (I recommend a 9x4x4inch Pullman Pan). Cover pan with plastic wrap.
9. Final Dough - Overnight Proof (10pm): Leave your dough to proof overnight at room temperature until it has tripled in volume and fills 90% of the tin, around 10-12 hours (at ~22C). Depending on how cool your kitchen is, this may take a little longer. If it's still not tripled by the morning, you can place the tin in the oven (turned off) with the light on or another warm area for an hour to speed up the proof.
10. Final Dough - Bake (8am Next Day): Pre-heat your oven to 180C/350F (160C/325F with convection). Once the dough is proofed, transfer to oven and bake for 35min, or until internal temp is >96C/195F. Check the loaf 15min into the bake - if it's browning too quickly, place a piece of foil over the top for the rest of the bake.
11. Final Dough - Enjoy: Remove from oven & brush a little extra melted butter onto the top if desired. Immediately turn the loaf out onto a cooling rack. Let cool completely and enjoy!