Instructions

for the sponge

Stir flour, water, and yeast in large bowl with wooden spoon until well combined. Cover tightly with plastic wrap and let sit at room temperature until sponge has risen and begins to collapse, about 6 hours (sponge can sit at room temperature for up to 24 hours).

for the pancetta mixture

Cook 4 ounces (113 grams) finely chopped pancetta in 12-inch skillet over medium heat, stirring occasionally, until well rendered, about 10 minutes. Using slotted spoon, transfer pancetta to medium bowl. Add 1 chopped red onion and 2 tablespoons water to fat left in skillet and cook over medium heat until onion is softened and lightly browned, about 12 minutes. Transfer onion to bowl with pancetta and stir in 2 teaspoons minced fresh oregano; let mixture cool completely before using.

for the dough

Stir flour, water, and yeast into sponge with wooden spoon until well combined. Cover bowl tightly with plastic; let dough rest for 15 minutes.
Stir 2 teaspoons salt into dough with wooden spoon until thoroughly incorporated, about 1 minute. Cover bowl tightly with plastic and let dough rest for 30 minutes.
Using greased bowl scraper or rubber spatula, fold dough over itself by gently lifting and folding edge of dough toward middle. Turn bowl 45 degrees and fold dough again; repeat turning bowl and folding dough 6 more times (total of 8 folds). Cover tightly with plastic and let rise for 30 minutes. Repeat folding and let dough rise for 30 minutes longer. Fold dough one final time, then cover bowl tightly with plastic and let dough rise until nearly doubled in size, 30 minutes to 1 hour.
One hour before baking, adjust oven rack to upper-middle position, place baking stone on rack, and heat oven to 500 degrees. Coat two 9-inch round cake pans with 2 tablespoons oil each. Sprinkle each pan with ½ teaspoon salt. Transfer dough to lightly floured counter and dust top with flour. Divide dough in half and cover loosely with greased plastic. Working with 1 piece of dough at a time (keep remaining piece covered), shape into 5-inch round by gently tucking under edges.
Place dough rounds seam side up in prepared pans. Coat tops and sides with oil, then flip rounds so seam side is down. Cover loosely with greased plastic and let dough rest for 5 minutes.
Using your fingertips, gently press each dough round into corners of pan, taking care not to tear dough. (If dough resists stretching, let it relax for 5 to 10 minutes before trying to stretch it again.) Using fork, poke surface of dough 25 to 30 times, popping any large bubbles. Sprinkle the pancetta mixture evenly over top of each loaf; cover loosely with greased plastic; and let dough rest until slightly bubbly, about 10 minutes.
Place pans on baking stone and reduce oven temperature to 450 degrees. Bake until tops are golden brown, 25 to 30 minutes, rotating pans halfway through baking. Let loaves cool in pans for 5 minutes. Remove loaves from pans and transfer to wire rack. Brush tops with any oil remaining in pans and let cool for 30 minutes. Serve warm or at room temperature.