- At least 1 hour before mixing dough, place dried mushrooms in medium-sized bowl and pour boiling water over to rehydrate. When ready to mix dough, remove mushrooms, squeezing vigorously to extract water. If rehydrated mushrooms are whole, coarsely chop and set aside.
- Pour cooled mushroom water into large bowl along with starter, being careful not to incorporate any sandy sediment that may have settled on bottom. Add flours and mix with hands until sticky, shaggy mass forms. Cover with plastic and let rest at room temperature for about 20 minutes, allowing flours to fully hydrate.
- Sprinkle salt over dough and mix thoroughly in with hands, making sure salt is completely incorporated. Fold in both rehydrated and fresh mushrooms and tarragon. Cover with plastic and allow to bulk ferment at room temperature for 4 hours, stretching and folding every 30 to 45 minutes.
- When dough is puffy and active, transfer to counter. Divide in half and pre-shape. Cover with plastic and allow to bench rest for 10 to 30 minutes. Final shape to your desired form and place seam-side up into floured bannetons or couche. Cover with towel and then plastic and refrigerate for up to 24 hours.
- Preheat Dutch oven to 500 degrees for 30 to 45 minutes.
- Cut out a circular piece of parchment paper. Dust with cornmeal. Turn loaf out onto cornmeal-dusted parchment paper and score top with lame. Carefully place into the preheated Dutch and position the lid. Lower the oven temperature to 480 and bake for 20 minutes. Remove the lid and allow to bake for another 15 to 20 minutes or until the crust is a deep dark brown and the loaf sounds hollow when thumped on the bottom. Note: If your oven runs hot, lower the temperature to 470 degrees and carefully remove the loaf from the Dutch oven after the initial 20 to 25 minutes of baking time.