¹/₃ cup warm water (110°F to 115°F)

¹/₄ oz active dry yeast

2-¹/₃ cups cake flour

2 cups all-purpose flour

¹/₃ cup granulated sugar

2-¹/₂ teaspoons fleur de sel

6 large eggs

2-¹/₂ sticks unsalted butter, cut into 1-inch cubes, at room temperature

Combine the water and yeast in a small bowl. Let stand for 10 minutes, then stir until the yeast is completely dissolved. Set Aside.

Sift together the flours, sugar and salt into the bowl of a stand mixer fitted with the dough hook. Add the eggs and beat for 1 minute at low speed, scraping down the sides with a rubber spatula as needed. Slowly add the dissolved yeast and continue beating at low speed for 5 minutes. Stop the machine, scrape any dough off the dough hook, and beat for another 5 minutes.

Add the butter cubes, about one-quarter of them at a time, beating for about 1 minute after each addition. Once all the butter has been added, beat for 10 minutes more, until the dough is smooth and silky.

Transfer the dough to a large floured bowl and cover with plastic wrap. Let stand in a warm place until doubled in size, about 3 hours.

Turn the dough out onto a generously floured work surface and gently work out the air bubbles by folding the dough over several times while lightly pressing down on it. Return the dough to the bowl, cover with plastic wrap, and refrigerate overnight.

Generously butter two loaf pans (8-¹/₂ by 4-¹/₂ by 3 inch) or one Pullman loaf pan. Turn the dough out onto a floured work surface. With floured hands, divide the dough in half, shape it into 2 rectangles that fit into the loaf pans, and put the dough in the pans. Let the dough rise, uncovered, in a warm place until it is about ¹/₂ inch above the top of the pans, about 3 hours.

Preheat the oven to 350°F.

Bake the brioche until it is well browned on top and sounds hollow when tapped, 35-40 minutes for 2 loaves, 45 to 50 minutes for a Pullman loaf. Remove from the oven and immediately turn the brioche out onto a cooling rack.

If serving immediately, let the bread cool for 10 minutes, then slice. If serving within a few hours or up to 2 days, promptly wrap the hot bread in aluminum foil and set aside at room temperature until ready to use. To freeze, wrap the hot bread in foil and promptly freeze. The bread can be frozen for up to 2 months; when ready to use, reheat (without thawing, and still wrapped in the foil) in a 250°F oven until heated through, 20 to 25 minutes.

If using the brioche for croutons or bread pudding, let sit at room temperature, uncovered, to dry for a day.