Make the Dough
In a medium bowl, combine the yeast with the warm water and 1 teaspoon of the sugar and let stand until foamy, about 5 minutes. Whisk in the 6 eggs. In the bowl of a standing mixer fitted with the dough hook, mix the 4 1/2 cups of sifted flour with the salt and the remaining 1/4 cup of sugar. Add the egg mixture and beat at medium speed until the dough is just moistened and very stiff. Add the butter a few cubes at a time, waiting until it is partially kneaded into the dough before adding more. Continue kneading until the butter is fully incorporated and the dough is silky, 8 to 10 minutes. Transfer the dough to an oiled bowl, cover with plastic wrap and refrigerate until chilled and slightly risen, at least 2 hours or overnight.