For a standard home sheet pan, build your dough up from 2-3 cups (473-710 ml) of water, depending on how thick you like your focaccia. I used a mini sheet pan and only one cup of water.
For every cup (237 ml) of water, use a teaspoon each of salt, honey, and dry yeast, and about 30 g (a big spoonful) of grated pecorino — combine all that. For every cup of water, I use a big spoonful of cornmeal and two big spoonfuls of whole wheat flour, and just enough bread flour to make it come into a dough.
Cover and let rise for a couple of hours at room temp, or put in the fridge for a day or two (a longer rise in the fridge will taste better). Don't be worried if the dough doesn't rise much.
Wet your hand, grab one side of the dough, stretch it out, and fold it back over on the dough — repeat a few times until the dough won't stretch easily anymore.
This dough tends to stick inside baking vessels, so if your pan doesn't have a nonstick coating, I recommend lining it with parchment paper.
Liberally oil the inside of your sheet pan (even if it's lined with parchment), put the dough in, and swish it around in the oil to get the pan and the dough fully coated. Stretch the dough out as flat as possible, which won't be much. Cover and let rise at room temperature for an hour or two until puffy.
Put a little more oil on top and use your fingertips to dock the dough while stretching it out into the corners of the pan. Top with some crunchy finishing salt.
Bake at 200°C until very brown on top and the bread feels like a stiff spring when you poke it — mine took 15 min. While you're waiting, peel and chop some garlic and fresh herbs. Melt a knob of butter in the microwave along with the garlic to cook it, then stir in the herbs.
When the bread is done, slide it out ASAP to a cooling rack to let the bottom steam out. Brush the top with the butter/garlic/herb mixture.