In a large airtight container, combine the yeast and sugar. Gradually add the lukewarm water while whisking vigorously to dissolve the sugar and yeast. Allow the mixture to sit for 10 minutes until it becomes frothy. If it doesn't bubble, the yeast may be expired or the water too hot, so start over with fresh yeast.

Once the yeast mixture is frothy, add the flour and then the salt, ensuring the salt doesn't directly touch the yeast. Mix everything with your hands until the dough is smooth, elastic, and free of lumps, which should take a few minutes.

Create small wells in the dough by pulling sections away from the edge of the container and pouring in a quarter of the olive oil. Repeat this process three more times around the dough until all the oil is incorporated. Fold the oil into the dough.

Visualize the dough as a clock face. Starting at 12 o'clock, fold the outer edge of the dough into the center, then do the same at 3 o'clock, 6 o'clock, and 9 o'clock. Repeat this folding technique two more times, then turn the dough seam-side down in the container. Seal it with a lid and refrigerate for 18 to 24 hours.

To bake, generously butter four stainless steel tins. Pour in ¼ cup of extra-virgin olive oil, ensuring it coats the sides and bottom of the tins. Remove the dough from the fridge and repeat the folding process starting at 12 o'clock and then at 6, 3, and 9 o'clock. Do this one more time, then place the dough seam-side down in the tin.

Gently stretch the dough without reaching the edges, allowing it to expand as it rises. Find a warm spot in your home and let the dough rise for 3 to 4 hours, or until it has doubled in size. If your home is cool, turn on the heating to help the dough rise.

Preheat your oven to 220°C with the fan on. Lightly oil your hands and drizzle about 1 tablespoon of oil over the focaccia, gently rubbing it over the surface while dimpling it with your fingertips to create small air bubbles. Sprinkle with 1 tablespoon of flaky salt and drizzle another tablespoon of olive oil on top.

Bake the focaccia in the oven for 30 minutes, then increase the temperature to 245°C and bake for an additional 10 minutes until the bottom is crispy and the top is a deep golden color. If the bottom remains soft, remove the focaccia from the tin and return it to the oven for 5 to 10 minutes at 220°C, placing the empty tin underneath to catch any drippings.

Allow the focaccia to cool in the tin for 5 minutes before transferring it to a cooling rack. Slice once it has cooled slightly, about 20 minutes later.