Step 1

Mix 1/2 cup bread flour, 1/4 cup water, and sourdough discard together with a wooden spoon. Add a little flour to the bowl of a stand mixer. Add starter mixture and allow to rise in a warm area, without direct sunlight, until doubled in size, about 2 hours.

Step 2

Attach dough hook and begin to mix the starter. Add remaining flour, 3 tablespoons oil, and 1 teaspoon salt. Mix in enough of the remaining water until dough pulls from the sides of the bowl and forms a ball; you may not need the full 3/4 cup. Knead dough in the mixer for 5 minutes.

Step 3

Transfer dough to a work surface and knead by hand for 5 minutes. Score and cover with a cloth. Allow to rise in a draft-free place until doubled in volume, at least 2 hours, and up to overnight.

Step 4

Lightly oil a shallow 12x16-inch baking pan. Knead dough for 5 minutes. Spread into the pan using your hands. Whisk 1 tablespoon oil and 1 tablespoon water together. Sprinkle a little bit over the focaccia. Cover with plastic wrap and let rise until doubled in height.

Step 5

Preheat the oven to 400 degrees F (200 degrees C).

Step 6

Push into the focaccia with your fingertips, leaving indentations about 1 1/2 inches apart. Evenly distribute olives and cherry tomatoes on top, pushing them into the dough. Sprinkle rosemary leaves and flaked salt on top. Sprinkle a little more of the oil-water mixture on top.

Step 7

Bake in the preheated oven until browned and cooked through, 20 to 25 minutes. Drizzle olive oil on top before serving.