In a bowl, mix whole-wheat flour, 1/2 cup all-purpose flour, soda, and salt. Add buttermilk, 1/3 cup oil, and molasses; stir until well moistened.
Rub a 9-inch cake pan with oil, then dust with all-purpose flour. Scrape the bread batter into the pan and spread level.
Bake in a 400° regular or convection oven until bread is well browned and just begins to pull from pan sides, 35 to 45 minutes. Let cool in pan at least 5 minutes. Cut loaf into wedges in pan or invert from pan, turn over, and cut into wedges.