In a large mixing bowl, whisk together the bread flour and whole wheat flour until evenly combined.
Add the sourdough starter and water to the flour and mix with your hand or a spatula until no dry bits remain and a rough, shaggy dough forms.
Cover the bowl and let the dough rest (autolyse) for 45–60 minutes at room temperature.
Sprinkle the salt over the dough and mix by pinching and folding until the salt is fully incorporated and the dough feels smoother.
Add the chopped olives and olive oil to the dough and gently fold until the olives are evenly distributed.
Begin bulk fermentation by covering the bowl and letting the dough rest at room temperature for 3–4 hours, depending on warmth.
During the first 90 minutes of bulk fermentation, perform 3–4 sets of stretch-and-folds every 30 minutes, pulling each side of the dough up and folding it over itself.
After the final stretch-and-fold, let the dough rest undisturbed for the remainder of bulk fermentation until it has risen by about 50% and shows bubbles along the sides.
Lightly flour your work surface and gently turn the dough out of the bowl.
Using a bench scraper, pre-shape the dough into a loose round by folding the edges toward the center and flipping it seam side down.
Let the pre-shaped dough rest on the counter, covered with a towel, for 20–30 minutes to relax.
Lightly flour the top of the dough, flip it over, and shape it into a tight boule or batard by folding and rolling to create surface tension.
Generously dust your proofing basket with a mixture of rice flour and wheat flour, or line a bowl with a well-floured towel.
Place the shaped dough seam side up in the prepared basket or bowl.
Cover the dough and let it proof at room temperature for 1–2 hours, or until slightly puffy, then refrigerate for 8–12 hours for cold retard (optional but recommended).
About 45 minutes before baking, place the Dutch oven with its lid into the oven and preheat to 250°C (480°F).
Cut a piece of parchment paper and place it over the proofed dough, then invert the basket to release the loaf onto the parchment, now seam side down.
Score the top of the dough with a lame or sharp knife to allow for controlled expansion.
Carefully remove the hot Dutch oven from the oven, lift the dough using the parchment, and place it inside the pot.
Cover with the lid and bake for 20 minutes at 250°C (480°F).
After 20 minutes, reduce the oven temperature to 230°C (450°F), remove the lid, and continue baking for 20–25 minutes until the crust is a deep golden brown.
Remove the loaf from the Dutch oven and place it on a wire rack to cool completely for at least 1–2 hours before slicing.