1. Combine Starter, Water, and Salt: In a large mixing bowl, gently whisk together the active sourdough starter, warm water, and sea salt until the salt is dissolved and the starter is mostly incorporated. The mixture will look milky and slightly frothy.

2. Add Flours and Mix Dough: Add the whole spelt flour and all-purpose flour to the wet ingredients. Use a sturdy spoon or your hands to mix until all the flour is hydrated and a shaggy, cohesive dough forms. There’s no need to knead extensively at this stage; just ensure no dry pockets of flour remain.

3. First Rise (Bulk Fermentation): Lightly grease another large bowl with olive oil. Transfer the dough to the greased bowl, turning it once to coat. Cover the bowl tightly with plastic wrap or a damp kitchen towel. Let the dough rise at room temperature (around 70-75 F) for 8-12 hours, or until it has noticeably increased in volume and looks bubbly. This can also be done overnight.

4. Shape the Loaf: Gently turn the dough out onto a lightly floured surface. Avoid deflating it too much. Gently stretch and fold the edges of the dough towards the center to create a round or oblong shape. You can also perform a series of gentle folds to build tension on the surface of the dough.

5. Second Rise (Proofing): Place the shaped dough into a floured banneton (proofing basket) or a bowl lined with a floured kitchen towel, seam-side up. Cover it loosely with plastic wrap or a damp towel. Let it proof at room temperature for 2-4 hours, or until it looks puffy and springs back slowly when gently poked. Alternatively, you can refrigerate it for 12-24 hours for a longer, colder proof, which can enhance flavor.

6. Preheat Oven and Baking Vessel: About 30 minutes before baking, place a Dutch oven with its lid into your oven and preheat to 450 F (232 C). Getting the Dutch oven very hot is crucial for a good crust.

7. Bake the Bread: Carefully remove the hot Dutch oven from the oven. Gently invert the proofed dough into the hot Dutch oven. If desired, score the top of the dough with a sharp knife or razor blade. Cover with the lid and bake for 30 minutes.

8. Finish Baking and Cool: After 30 minutes, remove the lid from the Dutch oven. Reduce the oven temperature to 425 F (220 C) and continue baking for another 10-15 minutes, or until the crust is deeply golden brown and the internal temperature reaches 200-210 F (93-99 C). Carefully remove the bread from the Dutch oven and transfer it to a wire rack to cool completely for at least 1-2 hours before slicing. This cooling step is vital for the crumb to set properly.