The night before, mix 1 1/5 cups (300 g) of flour, the water and the yeast. Mix everything nicely with a spoon or stirrer, cover the bowl tightly with a lid and leave in the fridge to rise for about 12-14 hours.
The next day, when you remove the bowl, you will see large bubbles. Leave it to sit for 30 minutes at room temperature. Then mix the dough with the remaining 1/3 cup (90 g) of flour, the salt and 2 tablespoons of olive oil. The final dough you get will be slightly denser than the previous one, but it will still be liquid and not for mixing.
Leave the dough to sit for 10 minutes and pour it into a greased, non-stick tray, being careful not to break the gluten crust. Leave it to rise again for about 2 hours or until doubled in volume. Then gently brush the surface with a mixture of olive oil and a little water and sprinkle it with coarse salt.
Put the Italian focaccia to bake in a preheated 419°F (215 °C) oven. Baking takes about 20-30 minutes.