In a medium bowl, stir together water, yeast, and honey to dissolve.
In a very large bowl, whisk flour and salt together to combine, then add yeast mixture and olive oil. Stir until just incorporated, then cover with plastic wrap and leave out at room temperature to ferment for 12 to 14 hours.
Spread oil on a rimmed baking sheet, release the dough from the bowl and place it onto the pan. Stretch the dough and dimple it with your fingers.
Make the brine by stirring together salt and water until dissolved. Pour the brine over the dough to fill dimples.
Proof the focaccia for 45 minutes until light and bubbly. Preheat the oven to 450°F.
Sprinkle focaccia with flaky salt and bake for 25 to 30 minutes. Finish browning the top crust and then cool on a rack.
Serve warm or at room temperature. To store, wrap in parchment and then keep in an airtight container. Toast or reheat leftover focaccia before serving.
