In a measuring cup, mix the sugar with a 1/2 cup of the warm water and yeast and let stand in a warm place for 5 minutes, or until frothy. If using fast-acting yeast, there is no need to let the mixture stand.
In a large bowl, sift together the flour and salt. Rub in the butter, and make a well in the center. If using olive oil instead of butter, pour the olive oil into the remaining 1 1/2 cups water. Pour in the yeast mixture and most of the remaining water (and the olive oil, if using). Mix to a loose dough, adding the remaining water if needed, plus extra if necessary.
Knead the mixture until the dough is smooth and springy to the touch, about 10 minutes. If kneading in an electric food mixer with a dough hook, 5 minutes is usually long enough.
Put the dough in a large oiled bowl. Cover the top tightly with plastic wrap, and place somewhere warm to rise, until it is doubled in size. This may take up to 2 or even (on a cold day) 3 hours.
Preheat the oven to 425 degrees F.
When the dough has more than doubled in size, punch down, and knead again for 2 to 3 minutes. Leave to relax for 10 minutes before you begin to shape the bread.
Shape the bread into loaves or rolls, and then transfer to a baking tray, and cover with a clean tea or dish towel. Allow to rise again in a warm place for 20 to 30 minutes, until the shaped dough has again doubled in size. When the dough has fully risen, it should leave a dent when you gently press the dough with your finger.
The bread is full of air at this point, and therefore very fragile, gently brush the loaf with egg wash and sprinkle with poppy or sesame seeds, if using, or dust lightly with flour for a rustic-looking loaf.
Bake in the oven for 30 to 45 minutes for a loaf, depending on its size, or 10 to 15 minutes for rolls, Turn the heat down to 400 degrees F, after 15 minutes for the remaining baking time. When baked, the bread should sound hollow when tapped on the base. Transfer the loaf to a wire rack to cool.
Slow rising gives bread an amazing texture and flavor, if you have the time I would recommend trying it. Use cold water instead of warm water, and then leave the dough to rise in a cool place, or refrigerator overnight. Then, when the dough is shaped, leave to rise again for 8 hours in a cool place.