Dissolve the yeast in a bowl with the water and 1 tablespoon of sugar. Leave covered in a warm place for 10 minutes. Sift the flour into a large bowl with the salt, add the remaining sugar, 5 eggs and leavened yeast.
Knead for 10 minutes until you get a smooth and elastic dough. Divide the butter into 10 parts and add them to the dough successively while kneading. Put the dough in a buttered bowl for 1 night in the refrigerator, covered with a towel.
Divide the risen dough into 3 pieces and form 3 wicks, each 17 3/4″ (45 cm) long. Braid the wicks together and place the brioche (similar to a panettone) in a buttered baking dish. Cover and wait for 1 hour to double its volume.
Brush the brioche with a beaten egg and sprinkle it with sugar. Put it to bake for 10 minutes on high heat, then reduce to 356°F (180 °C) and bake another 15 minutes.