100% Whole Wheat Sourdough Hamburger Buns

Steps

1. 1Prepare starter and yudane (night before): Mix the starter ingredients in a bowl or jar, cover, and let sit at room temperature for about 12 hours (overnight) until it has increased in size, has many bubbles on the top surface, and has a pleasant "yeasty" smell. To prepare the yudane, stir together the flour and boiling water until it forms a paste and all the dry flour is absorbed. Cover and refrigerate until the next morning.
2. 2Mix and rest (next morning): Into a stand mixer fitted with a dough hook, add prepared starter, yudane, whole wheat flour, egg, sugar, and milk. Mix on low speed for a couple of minutes until combined. Cover the dough, and allow it to rest for 30 minutes.
3. 3Add salt and butter and knead: After 30 minutes, add the salt and cold butter cubes and knead until the butter is thoroughly incorporated. Continue to knead on low speed for 12-15 more minutes until the dough becomes shiny, has a "taught" feeling, cleans itself off the bowl of the mixer, and forms a very thin windowpane when stretched with damp fingers. (You can knead dough by hand using slap-and-folds if you don't have a mixer.)
4. 4Bulk ferment: Form the dough into a ball, place in a bowl or straight-sided container and cover with a lid or plastic wrap. Leave at room temperature until doubled in volume. (The bulk rise took me 2 hours with a dough temp of 73°F and ambient temp of 75°F, for your reference.)
5. 5Divide and shape: Line two half sheet pans with parchment paper. Remove dough to a clean countertop and divide into 10 pieces (75g each). Degas the first piece by pressing it flat with your palm to remove any air bubbles. Shape into a ball, then tighten the ball by scooting the dough against the surface of the counter in a circular motion with your hand cupped over the dough. Lightly flour your hands as needed to prevent sticking. Repeat to shape remaining buns.
6. 6Proof: Arrange buns on the prepared pans, 5 to each pan. Cover loosely with plastic wrap to prevent the buns from drying out. Leave to proof until the buns have more-than doubled in size, relax outward, are soft to the touch, and slightly wobble when the pan is bumped (proofing took me 3 hours, 50 minutes at 75°F). Meanwhile, preheat oven to 425°F with two racks arranged in the center.
7. 7Egg wash, top, and bake: Whisk together egg wash ingredients. Gently brush egg wash over the surface of each bun, being careful not to deflate the buns. Sprinkle with sesame seeds, if desired. Bake both pans together for 10 minutes, then rotate pans and bake for an additional 6-8 minutes or until buns are golden brown. Transfer buns to a cooling rack. Allow to cool completely before slicing or storing. Buns are delicious toasted, and are even better on day 2. They freeze well for up to 3 months.