First, warm your water to around 35˚C then mix in your sugar and yeast. Let that sit for about 5 minutes until it begins to foam and bubble. This step isn't crucial but it will let you know if your yeast is still alive which is crucial for the air pockets in the focaccia.
Once the yeast mix is slightly bubbly, add in your flour and salt and mix just until it makes a smooth dough. The dough should be quite sticky so don't worry about adding more flour if it's sticking to the spoon.
Cover the bowl with a tea towel and place it either in the fridge overnight or in a warm place for a few hours until it doubles in size.
Knock the air out of the dough and lather a baking tray generously with olive oil. Tip the dough into the baking tray and with oiled hands, spread it out so it covers the whole tray.
Cover the tray with a tea towel again and set it aside for another hour until it's puffy and doubled in size. While it's proofing, preheat your oven to 210˚C.
Drizzle a good amount of olive oil all over the top and dimple the focaccia by pressing your fingers down the length of the dough. Sprinkle with salt.
Bake for 20-25 minutes or until it's golden and crispy on top and sounds hollow when tapped.