Remove ¼ cup of fed sourdough starter and combine it with ⅔ cup water and 1 cup all-purpose flour in a sealed container. Mix until you have a very wet dough.

Let it sit overnight at room temperature.

In a large mixing bowl, combine the Day 1 starter soak, 2 cups fed sourdough starter, 2 cups all-purpose flour, 2 cups whole wheat bread flour, and 2 teaspoons salt. Gradually add water until a smooth, slightly sticky dough forms.

Knead the dough on a floured surface for 5–7 minutes until elastic.

Rest the dough in a bowl, covered, for 4–6 hours or until doubled in size.

Preheat the oven to 350°F (175°C).

Divide the dough into thirds. Place one portion into an oiled baking pan, reserving the rest for later use.

Drizzle olive oil on top of the dough, scatter rosemary leaves, and sprinkle generously with flaky salt. Using your fingers, press deep dimples into the dough surface.

Bake for approximately 30 minutes or until golden brown on top.

Remove from the oven and finish with a final sprinkle of flaky salt. Let cool slightly before slicing or tearing.