1. **Mix Dough (Day 1):** In a large bowl, whisk together the bread flour, whole wheat flour, salt, and instant yeast. In a separate jug, mix the lukewarm water and olive oil.

2. **Combine:** Pour the wet ingredients into the dry ingredients. Mix with a wooden spoon or spatula just until a wet, sticky dough forms and no dry flour remains. Do not knead.

3. **Ferment:** Scrape down the sides of the bowl. Cover tightly with plastic wrap (or a shower cap) and a kitchen towel. Let it sit at room temperature for **18 hours**. The dough will bubble up, double in size, and develop a wobble.

4. **Prep for Shaping (Day 2):** Line one baking sheet with parchment paper. Line a second baking sheet (or work surface) with a clean kitchen towel and dust the towel *very liberally* with flour (this prevents sticking).

5. **Divide:** Uncover the bowl (the dough will be very sticky). Flour your hands and the top of the dough. Gently knock back the dough to release some gas, then turn it out onto a floured surface. Divide the dough into two equal pieces.

6. **Proof:** Shape each piece roughly into a ball or oblong shape and place them on the floured kitchen towel, spacing them apart. Dust the tops with more flour and cover with another towel. Let proof for 2 hours.

7. **Preheat:** About 30 minutes before baking, preheat your oven to 425°F (220°C).

8. **Shape & Bake:** Carefully uncover the loaves. Using the towel to help you, gently flip/turn each loaf over and stretch it slightly to about 16 inches long. Transfer them onto the parchment-lined baking sheet.

9. Bake for 35–40 minutes, or until the loaves are deep golden brown and sound hollow when tapped on the bottom.

10. **Cool:** Transfer to a wire rack and let cool completely before slicing to preserve the airy texture.