Topping:
12 ounces Onions, peeled
Powdered sugar, as needed
Kosher salt, as needed
Dough:
20 ounces All-Purpose Sponge (Poolisch), at room temperature
1 1/2 pounds Bread flour
3 ounces Dark rye flour
4 ounces Whole wheat flour
3/4 ounce Instant yeast
18 fluid ounces Water (temperature controlled)
1 ounce Salt
1 pound Old Dough (Pâte fermentée) (optional) at room temperature
6 ounces Walnuts, chopped
Yield: 4 Loaves
1. Cut the onions into 1/8-inch (3 millimeter) thick slices. Place them on paper-lined sheet pans. Lightly dust with powdered sugar and sprinkle with kosher salt. Bake the onions at 375°F (190°C) until lightly browned. Set aside.
2. Place the sponge, flours, instant yeast, water, and salt in the bowl of a mixer fitted with the dough hook. Mix on low speed to combine the ingredients. Then knead on medium speed until the dough is smooth and elastic and reaches 77°F (25°C) approximately 7 to 10 minutes.
3. Add the Old Dough, if using, in small pieces. Continue kneading until the dough is fully developed. Mix in 8 ounces (240 grams) of the cooked onions and the walnuts until combined.
4. Ferment the dough until doubled, approximately 1 hour.
5. Punch down and divide the dough into four uniform pieces. Shape into loaves and place seam side down on a floured canvas, banneton or sheet pan. Proof in a warm area until the loaves increase 50%, approximately 45 minutes to 1 hour.
6. Flip the loaves onto a baking sheet or peel, if necessary. Score and then garnish the top with the remaining onions. Bake at 425°F (222°C) with steam injected into the oven during the first few minutes of baking. Bake until golden brown, 40 to 45 minutes.
Notes: Method: Sponge and Old dough
Fermentation: Sponge and Old dough 4 to 6 hours. Final dough, about 1 hour. Proofing 45 minutes to one hour.