Prepare your brine: for 1Kg flour, 180ml lukewarm water, 2tbsp olive oil, 3 tbsp fleur de sel. Oil 2 thick baking sheets or shallow hotel pans and set aside.
Dump your dough over a table (smooth wood, marble or steel are the ideal surfaces) and keep a water-filled bowl handy: you will need to wet your fingers as you work the sticky dough. Using a bench scraper, divide the dough in half and round the two halves in balls, by working them up counter-clockwise either with your hands or the bench scraper and using the table surface to build tension.
Transfer each ball to a baking sheet, cover it and let rise at room temperature for an hour (make sure ambient temperature is warm enough: if not, turn on a burner, or place baking sheets near a radiator – but never in direct contact with them).
Using the ball of your fingertips gently spread each dough ball on the baking sheet, pushing the gas out as you go, particularly along the edges (if not degassed, they will rise too much during baking): make sure not to poke through the dough. Pour half the brine over the dough, cover and let rise for another hour at room temperature.
Preheat your oven at 500F, placing a Pyrex or oven safe metal container on the bottom. Pour the rest of the brine over your dough, gently pressing with your fingertips to create dimples, working from top to bottom with both hands at the same time.
When the oven is hot, pour water in the container on the bottom of the oven (this will create some much-needed steam) and bake your focaccia (either one sheet or both at the time, if oven is big enough), for 20-25 minutes. Ready when golden.