Makes 1 focaccia
2¼ teaspoons (or 1 package) active dry yeast
5 cups unbleached all-purpose flour plus additional for kneading
¼ cup plus 3 tablespoons extra-virgin olive oil
2 teaspoons salt
1 tablespoon fresh thyme, chopped fine
Zest of 2 lemons
1 teaspoon Maldon sea salt
In a large bowl or in the bowl of a stand mixer, stir together 12⁄3 cups lukewarm (105 to 115°F) water and yeast and let stand until creamy and foaming, about 5 minutes. Add 5 cups flour, ¼ cup oil, and 2 teaspoons salt and beat with paddle attachment at medium speed until a dough forms. Replace paddle with dough hook and knead dough at high speed until soft, smooth, and sticky, 3 to 4 minutes. **If mixing by hand, this process will take longer, so be patient.
Turn dough out onto a lightly floured surface and knead. If dough is sticky, sprinkle with 1 to 2 tablespoons more flour. Knead dough 1 minute (it will still be slightly sticky), then transfer to a lightly oiled bowl and turn dough to coat with oil. Let rise, covered with plastic wrap, at warm room temperature, until doubled in bulk, 1 to 1½ hours.
Press dough evenly into a generously oiled 15-by-10-by-1-inch baking pan. Let dough rise, covered completely with a kitchen towel, until doubled in bulk, about 1 hour.
Preheat oven to 425°F.
Stir together thyme and remaining 3 tablespoons oil. Make shallow indentations all over dough with your fingertips, then brush with thyme oil, letting it pool in indentations. Sprinkle lemon zest and sea salt evenly over focaccia and bake in middle of oven until golden, 20 to 25 minutes.
Once out of oven, immediately remove from pan and serve warm or at room temperature.