Caramelized Onion Bread
2 cups warm water, divided
1 1/2 teaspoons active dry yeast, divided
3 1/4 cups bread flour, divided
2 tablespoons olive oil
2 large onions, peeled and sliced into 1/4-inch rings
2 tablespoons brown sugar
1/2 cup whole-wheat flour
2 1/4 teaspoons salt
1/2 teaspoon ground black pepper
Preparing the sponge
Place 1/2 cup water (105°F to 115°F) in a small bowl. Sprinkle 1/2 teaspoon yeast over the water and let sit for 3 to 4 minutes, or until foamy. Mix in 1 cup of the bread flour. Cover with plastic wrap and let sit overnight in a cool, dry spot.
Caramelizing the onions
The onions can be prepared the day before. Heat oil in a large skillet over medium heat. Add onions and cook, stirring frequently, for 10 minutes, or until softened and golden brown. Sprinkle with brown sugar and cook another 5 to 10 minutes, stirring often. Onions should be dark brown, soft and sweet. Remove from heat and cool. Refrigerate until ready to make bread.
Preparing the dough
Place 1 cup water (105°F to 115°F) in a large mixing bowl. Sprinkle with remaining 1 teaspoon of yeast and let sit until foamy, about 3 to 4 minutes. Add sponge, remaining 2-1/4 cups bread flour, whole-wheat flour, salt and pepper. With the dough attachment for an electric mixer, mix dough for 2 minutes. Alternatively, beat vigorously with a wooden spoon for 8 to 10 minutes. Let dough rest for 15 minutes.
Add reserved caramelized onions and resume mixing for 12 to 14 minutes, or until dough is silky and elastic and pulls away from sides of bowl. The dough should be very wet and sticky, but still elastic. Transfer dough to a lightly oiled bowl and cover with a towel or plastic wrap. Let rise in a warm place for 1-1/2 hours, or until doubled in volume.
Turn a baking sheet upside down and sprinkle with flour and cornmeal; set aside. Turn dough onto a well-floured surface, handling it gently to preserve as much volume as possible, and cut into 2 equal pieces. Gently pull and stretch each piece of dough into a flat round, about 1-1/4 inches thick. Transfer to prepared baking sheet. Cover and let rise in a warm place for 45 minutes to 1 hour.
Preheat oven to 450°F. Place baking stone on the middle rack in oven to preheat.
Right before placing loaves in oven, quickly spritz water on oven walls with spray bottle. Immediately slide loaves onto hot stone. Bake for 16 to 18 minutes, or until bread browns. Transfer bread to a wire rack to cool.