In a large bowl, dissolve sugar in warm water. Stir in yeast and allow to sit until the mixture becomes frothy, about 5-10 minutes.
Add melted butter, salt, and half the flour to the yeast mixture. Mix until smooth. Gradually add the remaining flour to form a firm dough.
Turn the dough onto a floured surface and knead until smooth and elastic, about 6-9 minutes.
Place the dough in a greased bowl, turning once to coat. Cover with a damp cloth and let rise in a warm place until doubled, about 1 hour.
Punch down the dough and divide it into two equal parts. Shape each into a loaf and place in two greased 9x5-inch loaf pans.
Cover and let rise until doubled, about 30-45 minutes. Meanwhile, preheat oven to 375°F.
After they've risen, bake the loaves for 30 minutes, or until the top is golden brown and the loaf sounds hollow when tapped.