# What You Need:
→ Sourdough Starter
01 - 3.5 oz active sourdough starter (100% hydration)
→ Dough
02 - 14 oz bread flour
03 - 10 fl oz lukewarm water
04 - 0.35 oz fine sea salt
05 - 0.68 fl oz extra-virgin olive oil
→ Topping
06 - 2 medium yellow onions, thinly sliced
07 - 1 tbsp olive oil
08 - 1 tsp flaky sea salt
09 - 1 tsp fresh rosemary leaves
10 - Freshly ground black pepper to taste
# Steps:
01 - In a large bowl, mix the sourdough starter, bread flour, and lukewarm water until a shaggy dough forms. Cover and let rest for 30 minutes.
02 - Add salt and olive oil to the dough and mix thoroughly until fully incorporated.
03 - Over the next 2 hours, perform 3 to 4 sets of stretch and folds at 30-minute intervals to develop gluten strength.
04 - Cover the bowl and allow the dough to rise at room temperature for 6 to 8 hours until doubled in volume.
05 - Generously oil a 9x13-inch baking pan. Gently transfer the dough without deflating, then use oiled fingers to stretch and press it evenly to fit the pan.
06 - Cover the pan and refrigerate for 8 to 12 hours for optimal flavor development and texture.
07 - Heat 1 tbsp olive oil in a skillet over medium-low heat. Add sliced onions and cook, stirring occasionally, for 20 to 25 minutes until golden, soft, and caramelized. Cool completely.
08 - Remove the dough from the refrigerator and allow it to rest at room temperature for approximately 1 hour before baking.
09 - Preheat oven to 425°F. Dimple the dough surface with your fingertips, drizzle with additional olive oil, then distribute caramelized onions, sea salt, rosemary, and black pepper evenly across the top.
10 - Bake for 25 to 30 minutes until the focaccia achieves a golden-brown color with crisp edges.
11 - Allow the focaccia to cool slightly before slicing and serving warm.
