Step 1: In a large mixing bowl, combine the active potato flake sourdough starter, warm water, sugar, and vegetable oil. Stir until the sugar is mostly dissolved.
Step 2: Gradually add 4 cups of the bread flour and the salt. Stir with a wooden spoon or a heavy-duty mixer until a shaggy dough forms.
Step 3: Continue adding the remaining flour, 1/2 cup at a time, until the dough begins to pull away from the sides of the bowl.
Step 4: Turn the dough out onto a lightly floured surface and knead for 8-10 minutes, or until the dough is smooth and elastic.
Step 5: Place the dough in a large, lightly greased bowl. Cover with plastic wrap and let it rise in a warm, draft-free place for 8 to 12 hours (or overnight) until tripled in size.
Step 6: Gently punch down the dough and divide it into two equal portions. Shape each portion into a loaf and place into greased 9×5 inch loaf pans.
Step 7: Cover the pans and let the dough rise again for 4 to 6 hours, or until it has risen about 1 inch above the top of the pans.
Step 8: Preheat your oven to 350°F (175°C). Bake the loaves for 25 to 30 minutes until the tops are golden brown and the internal temperature reaches 190°F.
Step 9: Remove from the oven and immediately brush the tops with melted butter. Allow the bread to cool in the pans for 10 minutes before transferring to a wire rack to cool completely.