1. Combine Wet Ingredients: In a large mixing bowl, gently whisk together the active sourdough starter, warm water, honey (or maple syrup), and salt until well combined. The mixture should look milky and slightly frothy from the starter.

2. Add Dry Ingredients and Mix: Add the bread flour, whole wheat flour, rolled oats, flax seeds, and sunflower seeds to the wet mixture. Use a sturdy spoon or your hands to mix everything until a shaggy dough forms and no dry spots of flour remain. It will be sticky at this stage.

3. First Knead and Bulk Fermentation: Lightly grease another large bowl with olive oil. Turn the dough out onto a lightly floured surface and knead it for about 5-7 minutes until it starts to become more cohesive and less sticky. It doesn’t need to be perfectly smooth. 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 it rise at room temperature (around 70-75 F) for 8-12 hours, or until it has doubled in size and looks bubbly and airy. This is your bulk fermentation.

4. Shape the Loaf: Once the dough has completed its first rise, gently turn it out onto a lightly floured surface. Avoid deflating it too much. Gently shape it into a round or oval loaf. For a round loaf, gently pull the edges of the dough towards the center, then flip it over and cup your hands around it to create tension on the surface.

5. Second Rise (Proofing): Place the shaped dough into a floured banneton 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 cold proof it in the refrigerator for 8-16 hours for a deeper flavor development.

6. Preheat Oven and Score: About 30 minutes before baking, place a Dutch oven (with its lid) into your oven and preheat it to 450 F (230 C). Once preheated, carefully remove the hot Dutch oven. Gently invert the proofed dough into the hot Dutch oven. Using a sharp knife or a bread lame, score the top of the loaf with a design of your choice (a simple cross or a single slash works well).

7. Bake the Bread: Place the lid back on the Dutch oven and bake for 30 minutes. After 30 minutes, remove the lid 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).

8. Cool Completely: Carefully remove the bread from the Dutch oven and transfer it to a wire rack. It is crucial to let the loaf cool completely for at least 1-2 hours before slicing. This allows the internal structure to set and prevents a gummy texture.