In a large mixing bowl, combine warm water, sugar, and yeast. Let it sit until foamy, about 10 minutes.
Stir in butter and salt, then add the flour a cup at a time. Mix until a sticky dough forms.
Turn the dough out onto a floured surface and knead for 8–10 minutes, until smooth and elastic.
Place dough in a greased bowl, cover, and let it rise in a warm spot until doubled, about 1 hour.
Punch down the dough and shape into a loaf. Place in a greased 9x5 loaf pan.
Cover loosely and let rise again until it’s crowned about 1 inch over the top of the pan, 30–45 minutes.
Bake at 350°F (175°C) for 30–35 minutes, or until golden brown and hollow-sounding when tapped.
Cool on a wire rack before slicing—if you can wait that long.