Cut off one-third of dough; set aside. Lightly knead larger portion of dough 4 to 5 times; shape into a ball, and place in a well-greased 5 cup brioche mold. Shape smaller reserved portion of dough into a ball, rolling one end to form a tapered, teardrop shape. Set aside.
Using three floured fingers, press down into center of dough in brioche mold, touching bottom of mold. Enlarge this cavity to shape of tapered end of reserved dough ball. Place tapered end into cavity, rounding upper portion of teardrop to form a smooth ball. Cover and repeat rising procedure 1 hour or until doubled in bulk.
Combine egg yolk and milk, stirring well. Lightly brush mixture over top of brioche. Bake at 350° for 45 minutes or until golden brown. Remove bread from mold immediately; cool on wire rack.