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 the yeast mixture, then pour into the flour mixture and mix until smooth. Stir in the remaining flour ½ cup at a time to form a soft dough.
Turn the dough onto a lightly floured surface and knead until smooth and elastic, 8 to 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 to 2 hours.
Punch the dough down and place it onto a lightly floured surface. Divide the 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 to 1½ hours.
When ready to bake, preheat the oven to 375°F.
Bake for 25 to 35 minutes, until the loaves are golden brown and the internal temperature reaches 200°F. The bread should also sound hollow when tapped.
Remove the loaves from the pans and transfer them to wire racks to cool. Brush the tops with butter while warm, if desired.