Make The Dough. In a large bowl, whisk together the starter, water, sugar, and oil together with a fork. Add the flours and salt. Mix to combine. Finish by hand, until a rough dough forms. Cover with a damp towel and let rest for 30 minutes to 1 hour. Replenish starter with flour and water. After dough has rested, work the dough into a smooth ball, about 20 seconds. The dough will be supple and smooth when it comes together.
Bulk Rise. Cover the bowl with a damp towel and let rise at room temperature, 70oF, until double in size, about 8 to 10 hours. The dough will look nice and domed when ready.
Shape. Remove the dough onto a lightly floured work surface. Gently dimple the surface with our fingertips to release any large air bubbles. Roll the dough into a log, tucking the ends underneath. Let rest for 5 to 10 minutes. Meanwhile, lightly coat a 9-inch loaf pan with oil. With floured hands, cup the dough and pull it toward you to tighten its shape. Place into your local pan, seam side down.
Second Rise. Cover the dough and let rest until it has risen about 1 inch above the rim of the pan, about 1 1/2 hours to 2 hours, depending on room temperature. Near the end of the rising time, pre-heat your oven to 375F.
Bake. Bake the dough on the center rack in your 375F preheated oven for 40 to 45 minutes. When finished, remove the loaf from the oven and brush the crust with the melted butter. Cool in the pan for 10 minutes, then transfer the loaf to a wire rack to cool completely before slicing.