The day before:

Yudane:

1. In a bowl, combine 75g white whole wheat flour and boiling water and mix well with spatula or spoon. Cover tightly and place in the fridge for at least 4 hours or overnight.
2. The mixture will be stiff after mixing, and soft and pliable the next morning. Use directly from the fridge.

Levain:

1. In a small bowl, combine the sourdough starter, water and flour. Mix thoroughly to combine.
2. Cover and let the mixture rise at warm room temperature until doubled in size, about 8-12 hours, depending on the temperature in your kitchen.

Bake day:

1. Remove the yudane dough from the refrigerator and into pieces. Combine with the levain, milk, flours, and flaxseed meal in the bowl of a stand mixer. Mix on low speed for 2 minutes to incorporate.
2. Add the brown sugar and mix thoroughly. Add the butter and continue mixing for another 10 – 13 minutes or until the gluten is well developed and can be drawn out into a fairly transparent sheet (windowpane test).
3. The dough should be slightly on the wet side due to the whole grains. Scrape down the dough from the hook periodically during the kneading process to ensure well distributed gluten development.
4. Add the toasted sesame sesame seeds and mix thoroughly. Let the dough rest for 15 minutes.
5. Sprinkle the salt over the top of the dough and add the remaining 15 grams of milk. Mix on low speed until the salt is evenly distributed throughout the dough.
6. Cover, let the dough rest at warm room temperature. Check the dough after 45 minutes and stretch and fold if needed.
7. Continue to check the dough every 45 minutes until the dough is doubled in size, about 3-4 hours, depending on the temperature in your kitchen.
8. Divide the dough into 3 equal pieces and preshape lightly into rounds. Cover, let rest on the counter for 20 minutes.
9. Shape the rounds into tighter boules and place side-by-side in a greased or parchment-lined 8 ½ x 4 ½-inch glass loaf pan.
10. Cover, let the loaf proof in the pan at warm room temperature for 2-3 hours, or until doubled in size.
11. While the loaf is rising, preheat the oven to 350 F (175 C). When the loaf has doubled, brush with egg wash.
12. Bake the loaf for 30-35 minutes until golden and baked through (internal temperature should be at least 190 F.) Rotate the pan after 15 minutes for even baking.
13. Cool in the pan 10 minutes. Remove the loaf from the pan and finish cooling on a wire rack completely before slicing and serving.