- 5 tablespoons lukewarm milk (100 to 115 degrees)
- 1/2 ounce fresh yeast
- 1 pound 2 ounces all-purpose flour, plus more for forming dough
- 1 tablespoon coarse salt
- 6 large eggs
- 1 1/2 cups (3 sticks) unsalted butter, slightly softened, plus more for molds
- 1/4 cup superfine sugar
- 1 large egg yolk
- 1 tablespoon milk
- Nonstick cooking spray
Place the milk and yeast in a small bowl; stir to dissolve.
Place the flour, salt, and eggs in the bowl of an electric mixer fitted with the dough hook attachment; add yeast mixture and mix on low speed to combine and knead, about 5 minutes. Scrape down sides of bowl with a spatula; knead on medium speed until smooth and elastic, about 10 minutes.
In a large bowl, mix together butter and sugar. Add a few small pieces of butter mixture to dough; with the mixer on low, add remaining butter mixture, a little bit at a time. When all the butter mixture has been added, increase speed and continue mixing until smooth, shiny, comes away from the sides of the bowl, and is elastic, 6 to 10 minutes.
Butter a large bowl, transfer dough to prepared bowl, and cover with plastic wrap; let stand in a warm place until doubled in volume about 2 hours.
Lift dough from bowl and drop back into bowl to deflate; repeat process once or twice. Cover bowl and transfer to refrigerator to chill for at least 8 hours and up to overnight.
Butter two loaf pans that measure 8 1/2-by-4 1/2-inches across the top, and 7 1/2-by-3 1/2-inches across the base. Divide dough into 2 equal pieces. Divide each piece of dough into 8 equal pieces; form each piece into a ball. Place 8 balls of dough in each loaf pan, side-by-side.
In a small bowl, whisk together egg yolk and milk. Brush dough with egg yolk mixture, reserving remaining. Spray two pieces of plastic wrap with nonstick cooking spray; cover dough in both pans, cooking spray-side down and let stand in a warm place until doubled in volume, 1 1/2 to 2 hours.
Preheat oven to 400 degrees on a convection oven and 425 degrees on a conventional oven.
Brush each loaf very lightly with reserved egg yolk mixture. Transfer pans to oven and bake until brioche just begins to turn golden, about 15 minutes. Reduce temperature to 350 degrees on a convection oven and 375 degrees conventional oven and continue baking until deep golden brown and internal temperature reaches 205 degrees on an instant-read thermometer, 20 to 25 minutes more.
Remove from oven and let brioche cool in pans for 5 minutes. Unmold onto a wire rack and let cool completely.