1. 1. Combine Starter and Water: In a large mixing bowl, gently whisk together the active sourdough starter and warm water until the starter is mostly dissolved. This ensures even distribution throughout the dough.

2. 2. Mix in Flours and Seeds: Add the freshly milled whole wheat flour, freshly milled rye flour, bread flour, and mixed seeds to the bowl. Mix with a sturdy spoon or your hands until no dry spots remain and a shaggy dough forms. Cover the bowl with a damp cloth or plastic wrap and let it rest for 30 minutes (this is called autolyse, and it helps the flour hydrate).

3. 3. Incorporate Salt and Begin Folding: After the rest, sprinkle the salt over the dough. With wet hands, gently incorporate the salt by squeezing and folding the dough for a minute or two. Then, perform your first set of “stretch and folds.” Grab a portion of the dough from the edge, stretch it upwards, and fold it over the center. Rotate the bowl a quarter turn and repeat this process 3-4 times until the dough feels slightly more cohesive. Cover and let rest for 30 minutes.

4. 4. Continue with Stretch and Folds: Repeat the stretch and fold process three more times, with 30-minute rest periods in between each set. By the end of the fourth set, the dough should feel stronger, smoother, and more elastic. It will have developed some air pockets.

5. 5. Bulk Fermentation: After the final set of folds, cover the bowl and let the dough bulk ferment at room temperature for 3-5 hours, or until it has increased in volume by about 30-50% and looks bubbly. The exact time will depend on your kitchen’s temperature and the strength of your starter.

6. 6. Shape the Batard: Gently turn the dough out onto a lightly floured surface. Carefully preshape it into a loose round or rectangle, letting it rest for 15-20 minutes. Then, shape it into a batard (an oval shape). To do this, gently flatten the dough into a rectangle, fold the top third down to the middle, then the bottom third up and over the top. Gently roll it into a tight oval, creating tension on the surface.

7. 7. Cold Proofing: Lightly flour a proofing basket (banneton) or a bowl lined with a floured kitchen towel. Carefully transfer the shaped batard, seam-side up, into the basket. Cover it with plastic wrap and refrigerate for 8-12 hours, or up to 24 hours. This cold proofing develops flavor and makes the dough easier to handle.

8. 8. Bake the Bread: Preheat your oven to 450 F (232 C) with a Dutch oven inside for at least 30 minutes. Carefully remove the hot Dutch oven. Gently invert the cold dough from the proofing basket into the Dutch oven. Score the top of the dough with a sharp knife or razor blade (a single slash down the middle is classic for a batard). Cover the Dutch oven and bake for 30 minutes.

9. 9. Finish Baking: Remove the lid from the Dutch oven 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).

10. 10. Cool Completely: Carefully remove the bread from the Dutch oven and transfer it to a wire rack. Let it cool completely for at least 1-2 hours before slicing. This is crucial for the crumb to set properly and for the flavor to fully develop.