Dough:

1/2 cup (120 g) milk, lukewarm

1 (0.25-oz.) packet active dry yeast (2 1/4 tsp)

4 cups (480 g) all-purpose flour, divided, plus more for dusting

6 large eggs, room temperature

1/2 cup (100 g) granulated sugar

2 tsp kosher salt

1 cup (2 sticks) unsalted butter, softened, plus more for pans

Assembly:

1 large egg

1 Tbsp water

Kosher or sea salt

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Make the sponge: In the bowl of a stand mixer, combine milk, yeast, and 1 cup of flour. Mix with a spatula, cover, and let sit for 45 minutes until bubbly.
Add the eggs, sugar, salt, and remaining 3 cups of flour. Using the dough hook, mix on medium until combined, then increase to medium-high. Scrape the bowl as needed and mix 10–13 minutes until shiny and pulling away from the bowl.
With the mixer running, add the softened butter 1 tablespoon at a time, letting each piece incorporate fully. Continue 13–15 minutes.
Mix an additional 5–7 minutes until the dough passes the windowpane test. Cover and let rise until doubled, about 1 hour.
For overnight rise: Punch dough down, cover, refrigerate overnight, then let proof until doubled, up to 2 hours 30 minutes.
For same-day baking: Turn dough onto a floured surface, punch down, and divide in half. Cut each half into 6 pieces (12 total). Flatten each into a rectangle, fold like a letter, flatten again, then roll tightly into a log.
Grease two 8×5-inch loaf pans. Arrange 6 dough logs seam-side down in each pan. Cover and proof 1 to 1 1/2 hours, until doubled.
Preheat oven to 375°F. Whisk egg and water; brush over loaves and sprinkle lightly with salt.
Bake 30 minutes or until deeply golden and internal temperature reaches 190°–205°F.
Cool in the pan 5 minutes, then transfer to a cooling rack to cool completely.

Swap some all-purpose flour for bread flour for a chewier texture.

Add citrus zest, vanilla bean seeds, chocolate chips, or cinnamon sugar for variations.

Dough is naturally sticky—keep mixing until fully developed.

Overnight refrigeration improves flavor and makes shaping easier.