Step 1: Prepare the Caramelized Onions: Heat 2 tablespoons of olive oil in a large pan over medium-low heat. Add sliced onions and cook, stirring occasionally, for 25-40 minutes until deeply golden brown and very soft. Set aside to cool completely.
Step 2: Mix the Dough: In a large mixing bowl, combine your active sourdough starter, all-purpose flour, warm water, and salt. Stir until a shaggy dough forms and no dry spots remain.
Step 3: Autolyse: Cover the bowl with a damp cloth or plastic wrap and let the dough rest for 30 minutes to allow the flour to fully hydrate.
Step 4: Knead the Dough: Turn the dough out onto a lightly floured surface and knead for 5-10 minutes until it becomes smooth and elastic.
Step 5: Bulk Fermentation & Inclusions: Place the kneaded dough in a lightly oiled bowl. Perform a series of 'stretch and folds' every 30-45 minutes for the first 2-3 hours of bulk fermentation.
Step 6: Incorporate Onions and Cheese: During the second or third set of stretch and folds, gently fold in the cooled caramelized onions and grated Asiago cheese, distributing them evenly throughout the dough.
Step 7: Continue Bulk Fermentation: Allow the dough to bulk ferment at room temperature for a total of 4-8 hours, or until it has nearly doubled in size and feels airy.
Step 8: Shape the Dough: Gently turn the dough onto a lightly floured surface. Shape it into a round or oval loaf. Place it seam-side up in a well-floured banneton or a bowl lined with a floured kitchen towel.
Step 9: Cold Proof: Cover the banneton and refrigerate for 8-16 hours for the final cold proof. This develops flavor and makes the dough easier to handle and score.
Step 10: Preheat Oven: When ready to bake, preheat your oven to 450°F (230°C) with a Dutch oven inside for at least 30 minutes.
Step 11: Bake the Bread: Carefully remove the hot Dutch oven. Invert the dough into the Dutch oven, score the top with a sharp blade, and cover with the lid. Bake for 30 minutes.
Step 12: Finish Baking: Remove the lid and continue baking for another 15-25 minutes, or until the crust is deeply golden brown and the internal temperature is 200-210°F (93-99°C).
Step 13: Cool: Carefully transfer the baked loaf to a wire rack and let it cool completely for at least 1-2 hours before slicing. This is essential for the bread's texture and flavor.