In a large bowl, dissolve yeast and ½ teaspoon sugar in warm water; let stand until bubbles form on the surface.
In a large bowl, whisk together 3 cups flour and remaining 3 tablespoons sugar and the salt.
Stir oil into yeast mixture, then pour into flour mixture and mix until smooth. Stir in remaining flour ½ cup at a time to form a soft dough.
Turn dough onto a lightly floured surface and knead until smooth and elastic, 8-10 minutes. Place in a large, greased bowl, turning once to grease the top. Cover and let rise in a warm place until doubled in size, 1½-2 hours.
Punch dough down and place onto a lightly floured surface. Divide dough in half and shape each piece into a loaf.
Place in two greased 5-x-9-inch loaf pans. Cover and let rise in a warm place until doubled, 1-1½ hours.
When ready to bake, preheat the oven to 375 degrees F.
Bake loaves for 26-34 minutes, or until golden brown and bread has reached an internal temperature of 200 degrees F (bread should sound hollow when tapped).
Remove bread from pans and transfer to wire racks to cool. Brush tops with butter while warm.