Activate starter the night before. Mix together 20 grams of starter, 40 grams of both all-purpose flour and filtered water. Stir to combine and allow it to sit at room temperature for 8 hours or until it’s doubled in size. This will give you 100 grams of sourdough starter.
Mix. Add the honey, sourdough starter, warm milk, and salt to the bowl of your stand mixer with the whisk attachment added. Stir to combine.
Add flour and wheat gluten. Next, add the whole wheat flour and vital wheat gluten. Stir to combine.
Add butter. Add the melted and cooled butter. Stir to combine.
Half the flour. Add 2 cups of the all-purpose flour and continue to stir. This dough will be very wet.
Add rest of flour. Switch out the whisk attachment for the dough hook. Start to mix the rest of the all-purpose flour into the dough by adding about ⅓ cup of flour to the dough at a time, stirring in between each addition to incorporate the flour. You’ll know that enough flour has been added when the dough is tacky and comes away from the sides of the bowl when it is being mixed.
Knead. Set your stand mixer to medium speed and knead the dough for 3 minutes. You can also do this by hand by turning the dough out onto a clean, dry surface and kneading the dough by hand for 5-8 minutes. You may need some additional flour to keep the dough from sticking to the counter.
Grease bowl. Turn out the dough onto a clean surface, clean out your mixing bowl, and lightly grease it with baking spray.
Long Rise. Transfer the dough to the greased bowl, cover with a tea towel or plastic wrap, and place in a warm place for about 8-12 hours or until the dough has doubled in size. The best is overnight.
Prep pans. Prepare two bread pans by lightly greasing the pans and adding a sheet of parchment paper, leaving a slight overhang on both sides.
Divide and shape. Once the dough has doubled in size, turn the dough out onto a lightly floured surface and cut the dough in half. Shape one of the pieces of dough into a rectangle of about double the size of the bread pan. Then roll the dough up, tucking in the edges as you go to shape the dough into a loaf form. Place the dough into one of the prepared bread pans. Repeat this process with the other dough ball.
Rise. Place the loaves in a warm place for about an hour covered so they can rise.
Egg wash (optional). Prepare the egg wash by adding one egg and one tablespoon of water to a small bowl. Stir or whisk to incorporate the egg and the water together completely. Using a pastry brush, brush the tops of the loaves with the egg wash.
Preheat oven. About 45 minutes into the second rise, preheat the oven to 375°F.
Bake. Once the oven is preheated, bake the loaves for 40 minutes or until the top is golden brown.
Cool. Keep the bread in the loaf pans and cool on a wire cooling rack for 15 minutes. Remove the bread from the pans and cool on a cooling rack for another 15 minutes before cutting into the bread.