I use a recipe from "Baking with Julia", which I have revised slightly:
Makes 3 focaccias
2 cups lukewarm water
2 tablespoons instant yeast
1/4 cup olive oil
6-1/2 to 7 cups unbleached bread flour
4 teaspoons salt
Mixing the Dough: Whisk 1/2 cup of the water and the yeast together in the bowl of a mixer. Set the mixture aside for 5 minutes, until the yeast dissolves and turns creamy.
Meanwhile, pour 1-1/2 cups warm water into a large measuring cup, add the olive oil, and whisk to blend; set aside. Whisk the flour and salt together in a large bowl and set this aside as well.
Pour the water-oil mixture over the yeast and stir with the whisk to blend. Add about half of the flour and stir with a rubber spatula just to mix. Attach the dough hook, add the remaining flour, and mix on low speed for about 3 minutes, or until the dough just starts to come together. If the dough appears dry and a little stiff, add a few drops of warm water, scraping the bowl and hook if necessary to incorporate the water and create a soft dough. Increase the mixer speed to medium-high and continue to mix for about 10 minutes, scraping down the hook and sides of the bowl as needed, until you have a soft, slightly moist, extremely elastic dough that cleans the sides of the bowl. You will know that the dough is properly mixed when a piece can be stretched, without tearing, to create a "window," an almost transparent patch of dough.
First Rise Transfer the dough to a work surface and form it into a ball. Place the dough in an oiled bowl, turn it around to cover it with oil, and cover the bowl tightly with plastic wrap. Allow the dough to rise at room temperature until doubled in bulk, 1 to 1-1/2 hours.
Second Rise Fold the dough down on itself to deflate it and let it rise again until doubled and billowy, 45 minutes to 1 hour.
Shaping and Resting Fold the dough over on itself again to deflate it (as you do this, you can hear the bubbles squeak and pop) and turn it out onto a work surface. Using a metal dough scraper or a knife, cut the dough into 3 equal pieces. Shape each piece into a ball.
The dough needs to be refrigerated for between 24 and 36 hours. (It is this long refrigerated rest that gives the focaccia its characteristic chewy texture and surface bubbles.) Place each ball in an oiled gallon-size lock-top plastic bag and refrigerate.
About 1-1/2 hours before you plan to bake, remove the dough from the refrigerator and gently take the balls out of the oiled bags. (If you have a problem, cut the bags open with scissors to release the dough.) Place the dough on a lightly floured surface, dust the tops of the balls with flour, and cover loosely but completely with plastic (to avoid having the tops go crusty). Let rest for 1 hour, until the dough reaches a cool room temperature and feels spongy when prodded.
Herb-infused or other olive oil
Chopped fresh herbs, such as rosemary and/or thyme (2 to 3 tablespoons), and coarse sea salt
Position an oven rack in the lower third of the oven and preheat the oven to 450°F; If you have a baking stone, place it in the oven and preheat it too; dust a peel with cornmeal. Or line two baking sheets with parchment paper and dust the paper with cornmeal; set the baking sheets aside. Fill a spray bottle with water and set it aside as well.
Shaping the Dough Use your palm to press down gently on each piece of dough, causing bubbles to appear on the sides, then slit the bubbles with a single-edge razor blade to release the gases. Gently pull and stretch each piece of dough into a square about 10 inches across, taking care not to overwork the dough or handle it too roughly--you don't want to knock out the bubbles you've worked so hard to create. Let. the dough relax, covered, for about 10 minutes, then tidy up the edges with your hands.
Baking the Bread Transfer the foccacias to the cornmeal-dusted peel or the parchment-lined baking sheets. Use a single-edge razor blade to slash each square, cutting a tic-tac-toe pattern, or making 3 slashes in the center of the dough and enclosing them in 4 slashes to form a square with open corners. Brush the foccacias with olive oil, sprinkle with fresh herbs and coarse sea salt, and put them into the oven.
Bake the breads for 15 to 20 minutes, or until they are golden with a heavy speckling of small surface bubbles, spraying the oven with water three times during the first 8 minutes of baking. As soon as you remove the focaccias from the oven, brush them with a little additional olive oil and transfer them to a rack to cool before serving.