Mix all-purpose flour and bread flour in a large bowl.

Heat 3/4 cup of milk until lukewarm in a small saucepan.

Pour the warm milk into a medium bowl and stir in the yeast.

Let stand until the yeast dissolves and the milk becomes creamy and starts to bubble, about 5 minutes.

Stir in 1 1/2 cups of the mixed flours to create a sponge.

Cover with plastic wrap and let the sponge stand until slightly risen, about 20 minutes.

Scrape the sponge into the bowl of a standing electric mixer fitted with a dough hook.

Add the sugar, salt, eggs and the remaining 2 cups of milk and beat at medium speed until blended.

Carefully add the remaining 6 1/2 cups of flour.

Beat at low speed until the flour is just incorporated, then knead at medium speed until the dough is evenly combined, about 5 minutes, scraping down the sides of the bowl occasionally.

Add the softened butter and continue to knead until the dough is very soft and silky, about 10 minutes longer.

Lightly butter a large bowl.

Transfer the dough to the bowl and cover with oiled plastic wrap.

Let the dough stand in a warm, draft-free spot until doubled in bulk, about 1 hour.

Punch down the dough.

Cover and let the dough rise until doubled in bulk again, about 1 hour longer.

Punch down the dough and turn it out onto a heavily floured work surface.

Divide the dough into 3 equal pieces.

Let rest on a lightly floured work surface for 20 minutes.

Butter three 8-by-4-inch loaf pans.

Form each piece of dough into a loaf shape about the same size as the pans.

Brush off any excess flour from the loaves and gently ease them into the pans.

Cover the pans loosely with oiled plastic wrap.

Let stand in a warm, draft-free spot until the dough rises 1 1/2 inches above the rims, about 45 minutes.

Preheat the oven to 350°F.

Mix the egg yolk with the cream to make an egg wash in a small bowl.

Brush the loaves with the egg wash.

Bake in the center of the oven for 1 hour, or until the tops are golden brown.

Turn the loaves out of the pans onto a wire rack.

Tap the bottom of the loaves; if they don't sound hollow, return the loaves to the pans and bake for a few minutes longer.

Let the bread cool completely on wire racks before slicing.