To a small container add the lukewarm water, instant dry yeast, and sugar. Stir and let the yeast activate (bloom) for 2 minutes.
To a large mixing bowl add the flour and the salt. Stir the flours together with a wooden spoon then add the yeast mixture.
Mix the ingredients together with a wooden spoon or with a silicone spatula until you have a wet and sticky dough. Roughly shape the dough into a ball and lightly drizzle with olive oil before putting it to proof.mi
PROOFING THE DOUGH
Quick proofing: cover the bowl with a damp cloth, leaving enough space between the dough and the cloth. Proof in a slightly warm oven for one and a half to two hours. The dough should double in volume.
Slow proofing: Cover the bowl with a damp cloth or with plastic wrap and let the dough rise and mature slowly in the fridge for 8 to 36 hours.
FOLD THE DOUGH
After proofing, fold the dough over on itself from the outside to the inside, still in the bowl and with a spatula (or with a spoon).
There's no need to touch it with your hands. Fold it 20 times. This will take about 30 seconds. Folding gives structure to the dough.
SHAPE AND SECOND PROOFING
To make thick, bready focaccia, use an 11 inch (28 cm) round baking pan or a 10 x 10 inch (25 x 25 cm) squared one.
To make a thin, crisp, pizza-like focaccia use a 15 x 10 inch (38 x 25 cm) or larger baking pan.
Grease your baking tray with a generous tablespoon of olive oil. Try to use a baking tray with a nonstick coating.
Focaccia tends to stick to the tray. If you want to reduce the amount of oil you can line your baking tray with parchment paper.
Transfer the dough to the center of the baking tray, then with the back of two spoons (or two spatulas) spread the dough out until almost the whole tray is evenly covered.
The dough is elastic at this stage and will pull back so don't worry if it doesn't cover the tray completely.
To prevent the spoons from sticking to the dough, wet the spoons with water. If the focaccia gets a little wet it's even better.
Put back in the slightly warm oven to proof for another 45 minutes to 1 hour, this time without covering it. We let the dough rise a second time to improve texture, make it lighter, and airy.
After this second proofing, take it out of the oven and preheat the oven to 450F or 230C.
ADD TOPPING
In a small bowl mix 1 tablespoon of olive oil, 3 tablespoons of water, and ½ a teaspoon of salt. Stir well and set aside.
After the second proofing, lightly oil your fingers on both hands and sink the fingers in the focaccia making dimples across the dough.
With a spoon, drizzle the oil, water, and salt mixture all over the focaccia, allowing the liquid to go into all the crevices.
Add rosemary on top, fresh or dry is up to you, and sprinkle with either flaky salt (like Malden salt) or coarse salt. Regular salt works too if you don't have those fancier salts.
BAKE
When the oven has reached temperature, place the focaccia in the medium-low rack of the oven and bake it for about 18 to 25 minutes.
The focaccia is cooked when it's golden brown and crispy on top, well-cooked on the bottom, but still soft inside.
Let it cool down for 5 to 10 minutes before removing it from the pan, cutting it, and serving it.