Mix the bread flour, whole wheat flour, and warm water in a bowl until no dry spots remain. Cover and rest for 45 minutes.

Add the starter, salt, and olives. Squeeze and fold for 3 minutes until the starter is fully worked in and the olives are evenly distributed.

Cover and bulk ferment at room temperature for 4 to 5 hours. Perform 4 sets of stretch and folds at 30-minute intervals during the first 2 hours.

Turn the dough onto a lightly floured surface and shape into a tight round. Place seam side up in a floured banneton, cover, and proof for 1 to 2 hours until the dough passes the poke test.

Preheat a Dutch oven at 450 °F (230 °C) for at least 30 minutes. Turn the dough onto parchment, score a deep slash, and bake covered for 30 minutes. Remove the lid and bake another 18 to 22 minutes until deeply amber.

Cool on a wire rack for at least 1 hour before slicing. Use a serrated knife and enjoy the crackle.