Combine flour and sugar in a large mixing bowl. Make a well in center of mixture; add yeast and water in center. Let stand 5 minutes.
Beat at low speed with an electric mixer until blended; add salt and 8 eggs, one at a time, beating until blended after each addition. Add butter gradually, beating well (small bits of butter will be visible). Cover and refrigerate 8 hours or overnight (dough will be sticky).
Divide dough into 12 portions; pinch off a 1-inch ball of dough from each portion, and set aside.
Roll larger pieces into balls on a lightly floured surface; place in well-greased individual brioche molds or a muffin pan. Place molds or muffin pan on a baking sheet.
Make a well in center of each ball. Shape remaining dough pieces into balls, and place in wells.
Brush brioche with beaten egg; let stand 30 minutes.
Bake at 350° for 30 minutes. Cool in molds 10 minutes; remove from molds.