Place the flour & water into the bowl of a stand mixer then mix until just combined. Cover & leave to autolyse for 1 hour.
Sprinkle the yeast over the dough then using a dough hook, mix to incorporate. This will take 1-2 minutes on a medium speed.
Next, add in the salt & olive oil then continue mixing on a medium speed until the dough starts to come away from the sides of the bowl. This will take at least 10 minutes.
Transfer the dough to a lightly oiled mixing bowl & leave at room temperature for 1 hour. During this hour, coil fold the dough every 15 minutes.This dough has a high level of hydration (around 90%) so will seem quite sticky. Don't worry, this is normal! The dough will become easier to work with as we fold it. Whilst the dough is proving, line a 9”x13” baking tin with baking paper then pour 1 tbsp of olive oil into the bottom of the tin.
Once the dough has proved for an hour, give it one last set of coil folds then transfer it into the lined tin. Cover loosely with clingfilm then leave to prove at room temperature for 45 minutes - 1 hour, until the dough has doubled in size.
In the meantime, preheat an oven to 220°c/200°c fan (428°f/392°f).
When the dough has risen, drizzle 2 tbsp of olive oil over the top then use your fingers to dimple the dough all over. Sprinkle a generous amount of sea salt over the focaccia then bake for 25-30 minutes, until the bread is a deep, golden brown.
Once baked, let the bread cool in the tin for 30 minutes then transfer to a wire cooling rack & leave to cool completely.