In a bowl, mix the yeast, a pinch of the sugar and 1/2 cup of the water and let stand until foamy. Stir in the egg, salt and the remaining sugar and 1 1/2 cups of water. Add 5 cups of the flour and stir to form a soft, sticky dough. Stir in the stick of softened butter. Add the remaining 1 cup of flour and stir. When the dough becomes too stiff, scrape it out onto a work surface and knead until smooth; add a few tablespoons of flour if necessary to keep the dough from sticking. Transfer the dough to a lightly buttered bowl, cover with plastic wrap and let rise in a draft-free place until doubled in bulk, 1 hour.