While dough is rising, decide whether you want the focaccia to be thick (soft in the middle and easy to slice in half for sandwiches) or thin (more crisp and good for dipping in hummus, marinara or soup, or just snacking.
If you want it thicker, butter a 13x9 pan well (including sides) and then pour 1T oil into center of pan and spread it over the butter, covering the whole pan, including sides.
If you want it thinner, butter and oil a half sheet pan the same way.
When dough has risen, leave it in the bowl and visualize it as quarters. Take 2 forks to pick up the edge of one quarter and fold it into the center. Rotate bowl ¼ turn and repeat until you've folded in all 4 edges once.
Turn dough into desired pan, and pour over any oil remaining in the bowl. With lightly oiled hands, press out almost into corners of pans. Allow to rise again on counter or in oven as before until doubled again - 1½-2 hours.
Preheat oven to 450°
To test if it's ready to bake, poke your finger into the dough. If it springs back quickly, it's not ready. If it springs back slowly, leaving an indentation in the dough, it's ready.
Form your fingers like you're holding a melon or ball and poke them into the dough all over, creating a deeply pocked surface.
Drizzle over the last tablespoon of oil and sprinkle surface with flaky sea salt. Bake until well browned, about 30 mins.