In the bowl of a stand mixer or a large bowl, add water and yeast, mix. Allow to sit until bubbly, about 10-15 minutes.
Stir in the olive oil, flour and sea alt with a spatula. Mix until things start to come together. If using herbs, you can mix them in now.
With a mixer and dough hook, knead the dough on medium-high for 5 minutes, until smooth. Or, knead by hand on an floured surface for about 10 minutes. After this kneading step, allow the dough to rest for 10 minutes.
Mix again on medium-high for 10-15 minutes, or by hand on a floured surface for 15 minutes, until the dough is smooth and starts to pull away from the bowl. It is OK if it is still very sticky - it should be! But the dough should be forming, and will be partially wound around the dough hook. You can do the windowpane test if desired.
Remove bowl from mixer, and get all the dough in the bowl. Oil your hands, and drizzle oil on top of the dough mass. Using your hands, work the dough into a ball-shape (doesn't need to be perfect), and scrape the sides of the bowl clean - get all the dough into one ball.
Cover the bowl with a towel, and allow to rise for 1 1/2 to 2 hours, until it is double in size.
Oil or wet you hands, and gently scoop them around the puffed dough ball. Lift the dough and allow it to fall on itself. Release the dough, turn the bowl about a quarter turn, and repeat. Do this a total of three times.
Allow the dough to rest as you prepare the pan for baking the focaccia in. Generously apply olive oil to a half sheet pan, using your hands to get it on all surfaces. You want a visible layer of olive oil shining back at you!
Without washing your hands, transfer the dough onto the greased sheet pan. Gently coax it into the pan. It will fight back - so let it rest for 10 minutes.
After 10 minutes, finish coaxing and pressing the dough into an even thickness. The top of the dough should be quite oily, if not, apply a bit more oil, then cover with plastic wrap.
Allow to rise in the fridge for 12-24 hours (or, to bake the same day: allow the dough to rise at room temperature for a final 45 minutes to 1 hour, until very puffy and large bubbles form).
To bake, pre-heat oven to 450F. Arrange a rack in the bottom third and top third of the oven.
Dimple the focaccia: drizzle olive oil over the top of the dough, and using your fingers, press down into the dough surface. Repeat until the dough is evenly dimpled. Scatter the coarse sea salt over the top of the dough.
Bake for 20-25 minutes on the bottom rack, then 5-10 minutes on the top rack, until golden brown.
Allow to cool until you can touch it, then remove from pan by using a thin spatula or off-set spatula. Cut into pieces and enjoy.