Put about 1 C starter in a large bowl. Feed with about 1/2 C each water and flour. Mix well. Cover and let stand until bubbly (2 hours at 70° ambient temp).
Sourdough starter, named yIH, just celebrated 2nd birthday.
Stir in about 1 C whole wheat flour. Add all purpose flour and coarse salt (about a palmful) and knead briefly and form a ball, place in an oiled bowl, flip ball to coat with oil. Mist with water, cover and let rise until doubled (overnight).
Place a piece of parchment inside a cast iron Dutch oven. Turn onto floured board and knead with wet hands. Form a ball (AKA round loaf AKA boule) and place in Dutch oven. Mist with water, cover pot and let rest 45 minutes.
Preheat oven to 450°. Slash the loaf with a sharp knife, mist, cover and place the pot in to oven. Bake 20 minutes. Lower heat to 400°. Brush loaf with oil to enhance browning and bake uncovered for 20 minutes. Remove from oven but leave in pot for 20 minutes. Lift using parchment, and place on a cooling rack.