In a large bowl, combine the flour and sugar. Peel and cut the potatoes into cubes, then boil them for about 14 minutes after the water starts boiling.

Drain the potatoes and let them cool in a colander. Meanwhile, dissolve the recently refreshed sourdough starter in the warm water.

Once the potatoes are cool, mash them thoroughly so there are no lumps. Add the mashed potatoes to the flour, then pour in the sourdough-water mixture and the olive oil. Mix until the flour absorbs the water and the mixture looks sandy. Cover the bowl with plastic wrap, a lid, or a clean towel and let it rest for about 30 minutes.

Knead the dough until it forms a smooth, fairly soft ball. If it's too sticky, add a little more flour. Add the salt and knead it in well by hand. Grease a bowl with olive oil, transfer the dough to it, and let it rest for a couple of hours in a turned-off oven, then refrigerate overnight.

The dough should double in size. Transfer it to a greased work surface and divide it into 8 equal pieces. Shape each piece into a ball. Place the balls on two baking sheets (4 balls per sheet) and gently flatten them to form focaccine. Let them rest and rise for another 4 hours.

With oiled fingers, make dimples in each focaccina. Use extra olive oil to coat your hands so some oil pools in the dimples. Drizzle more olive oil over the top for extra flavor. Top as desired: I made 4 with Taggiasca olives, 2 with dried oregano, and 2 with fresh rosemary. Sprinkle with flaky sea salt and bake in a convection oven at 430°F (220°C) for 18–20 minutes or until golden brown. Let cool and enjoy.