About 8 hours before you want to mix your dough. Make sure to feed your starter 1 cup of warm water, 3/4 cup of sugar, and 3 tablespoons of instant potato flakes. Allow it to feed and become nice and active before mixing up your dough.
In the bowl of your stand mixer, combine the flour, salt, active potato flake starter, warm warmer. and olive oil. .
Using your dough hook attachment, knead the dough for about 5 minutes on low. Dough should be smooth and slightly tacky. You can also do this by hand. If doing it by hand, knead for about 10 minutes.
Place into an oiled bowl and lightly drizzle the the top with about 1 Tbsp of olive oil. Cover with plastic wrap to prevent it from drying out. Allow to rise in a warm place for about 8 hours, or until double in size. This could take up to 15 hours or more depending on the temperature of your home.
Drizzle about 1 tablespoon of olive oil onto each of the 9 inch round pans and spread it evenly. Divide the dough, but handle the dough gently, trying to deflate all of the air bubbles. Transfer each half of the risen dough onto the prepared baking pans and gently press it out to fit the pan using your fingers to gently dimple as your stretch the dough into the pans. If the dough resists, let it rest for a few minutes to relax the gluten, then try again.
Cover the dough with plastic wrap and let it rise again for about 6-8 hours or until double in size again.
Preheat your oven to 400 degrees. Once the dough has risen for the second time, drizzle some more olive oil over the top, sprinkle with sea salt and add rosemary. Gently use your fingers to make dimples all over the surface trying not to pop any of the larger bubbles. You can get creative and add any other toppings of your choice!
Place the pans in the preheated oven and bake for 20-25 minutes, or until the focaccia is golden brown on top and sounds hollow when tapped on the bottom.
Allow the focaccia to stay in the pans for about 10 minutes and then use a spatula to gently remove from the pans. They should not stick if it was oiled well. Place the focaccia on a wire rack for it to cool slightly before slicing and serving.