In the bowl of a stand mixer fitted with a dough hook*, combine warm water and granulated sugar. Sprinkle yeast on top and let sit for 5 minutes until foamy. If the yeast does not foam, it is dead and you will need to start over with fresh yeast.
Add flour, sourdough discard, salt and black pepper and mix on low until combined and no dry spots remain. This will be a very shaggy, wet dough that you could not knead if you tried.
Transfer the dough to a large, oiled bowl and cover with plastic wrap. Let rise for 2-3 hours, until doubled in size.
Brush a 9x13-inch pan with 2-3 Tablespoons olive oil and set aside.**
Once the dough has risen, use a spatula to scrape around the perimeter of the bowl, deflating the dough. Transfer the dough to the center of the prepared 9x13-inch pan. Dip your fingers in olive oil, then use your fingers to press the dough until it reaches the edges of the pan. Cover with plastic wrap or a clean kitchen towel and let rise for 1 ½-2 hours, until doubled in size.
Preheat the oven to 450°F. Drizzle the dough with 2 Tablespoons olive oil. Lightly oil your hands and press deep dimples all over the dough, through to the bottom of the pan. Sprinkle with flaky sea salt.
Bake for 25-30 minutes, until the focaccia is golden and crusty. Drizzle with an additional 1-2 Tablespoons olive oil. Let cool for 10 minutes in the pan, then transfer to a cooling rack to cool fully. Slice, then serve.
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Notes
*You can make this recipe without a stand mixer. To do so, mix the dough in a large bowl with a wooden spoon until no dry spots remain. Keep in mind that the dough will be very wet (you could not knead this if you tried). To make this recipe with active sourdough starter, omit the yeast and replace the sourdough discard with active starter (200g). You will also need to increase the rise times. **Sourdough Discard Focaccia Muffins: You can make mini focaccias in a muffin pan! To do so, divide the dough into 24 greased muffin cups after the first rise. This will be less than ¼ cup of dough per muffin cup. After the second rise, dimple and sprinkle with flaky sea salt, then bake for 20-25 minutes.