In the bowl of a stand mixer, whisk together the starter, warm water, sugar, and olive oil until the starter is mostly dissolved.
Add the bread flour, all-purpose flour, and salt.
Mix on low speed with the dough hook until the dough forms a sticky, shaggy mass (about 2–3 minutes). If mixing by hand, stir until combined, then knead until the dough feels sticky and slightly elastic.
Cover with a plate or damp towel and let the dough rest for 30 minutes.
After the rest, turn the dough out onto a lightly floured surface. Knead briefly (less than a minute) until the dough is soft and slightly smooth. Place it into a greased bowl or bulk fermentation container. Cover and let rise at room temperature until doubled in size, about 6–8 hours depending on the warmth of your kitchen. The dough is ready when it passes the poke test.
Lightly oil your loaf pan. Gently turn the dough out onto a lightly floured surface. Shape it into a rectangle, pressing out any large air bubbles. Roll it into a tight log, tucking the ends underneath. Gently pull the loaf toward you to create surface tension, then place it seam-side down in the pan.
Cover with plastic film or a damp towel and let rise 1–2 hours, or until the dough is just peeking over the top edge of the pan.
Preheat your oven to 375°F (190°C).
Bake the loaf in the center of the oven for 40–45 minutes, or until golden brown on top and the internal temperature reaches 200°F (93°C). Let cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.
Notes
For a slightly softer crust, brush the top with melted butter while the bread is still warm.Store cooled bread in a bread box or tightly wrapped at room temperature for up to 3 days or freeze in slices for easy toast later.You can bake this in a Pullman pan (like the one I've linked above) for perfectly square sandwich slices. Just leave the lid off if you want a more rounded loaf like the photos in this post, or leave the lid on if you're aiming for a closed-top loaf.This bread recipe is pretty fool proof and even if it is over or under proofed, it is still delicious.