Combine all the flours (all-purpose, semolina, and high-gluten) in a bowl. From this mixture, take 1/3 cup (50 grams) and place it into a separate bowl to form the starter. Add 1/4 cup minus 1 tablespoon (50 grams) of water, taken from the total water amount, and the instant yeast to the set-aside flour. Mix until no dry flour remains. Let the starter sit, uncovered, for 1 hour, until bubbly and doubled in size.

In a large bowl, combine the remaining flour mixture, remaining water, bubbly starter from Step 1, the cooked and peeled potato (using a ricer or grater), extra-virgin olive oil, and fine salt. Mix with a spatula to combine, then knead by hand for 5-6 minutes, or use a stand mixer for up to 4 minutes, alternating between low and medium speed. If the dough feels too sticky, add a bit more flour as needed. The dough should feel very soft and come together in a ball with a light dusting of flour. I find that using a potato ricer gives the focaccia a lovely texture.

Transfer the kneaded dough to a clean bowl. Using a knife, score a cross on the surface of the dough. Allow it to rise in a warm place, such as a turned-off oven, for 1 hour to 90 minutes or until it has doubled in size.

Generously oil the focaccia pan with your hands. With your oiled hands, remove the risen dough from the bowl and transfer it onto the pan. Gently spread the dough to evenly cover the entire surface, using your fingertips. Cover with foil or plastic wrap and a kitchen towel, and allow it to rest for 10 to 30 minutes based on room temperature. The dough should rise a little, creating room to hold the toppings.

Slice the cherry tomatoes in half, then gently squeeze each half over the dough to let the juices flow onto the surface. Press the tomato halves into the dough. Fill any remaining areas with black olives. Sprinkle generously with dried oregano and drizzle with extra-virgin olive oil. Cover and let the focaccia rise for a final 15–30 minutes, depending on room temperature. I like to gently press the olives and tomatoes so they partially sink into the dough.

Preheat your oven to 465°F (240°C) with a convection/fan setting. Just before baking, sprinkle a few pinches of flaky sea salt on top of the dough. Bake the focaccia for 15–20 minutes, or until a golden crust forms and the tomatoes are nicely charred. If your oven does not have a fan, bake at 482°F (250°C) for 20–25 minutes. Allow the focaccia to cool slightly before slicing. For a more pronounced flavor, I sometimes add an extra drizzle of olive oil right after baking.