Instructions

1. Special equipment: a standing electric mixer with paddle attachment and dough hook.
2. Stir together 1 2/3 cups lukewarm (105-115 degree) water and yeast in bowl of mixer and let stand until creamy, about 5 minutes. Add 5 cups flour, 1/4 cup oil and 2 1/2 tsp table 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, 3-4 minutes.
3. Turn dough out onto a lightly floured surface and knead in 1-2 Tbsp more flour. Knead dough 1 minute (it will 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 1 1/2 hours.
4. Press dough evenly into a generously oiled 15x10 inch baking pan. Let dough rise, covered completely with a kitchen towel, until doubled in bulk, about 1 hour.
5. Preheat oven to 425 degrees.
6. Stir together rosemary and remaining 3 Tbsp oil. Make shallow indentations all over dough with fingertips then brush with rosemary oil, letting it pool in indentations. Sprinkle sea salt evenly over focaccia and bake in middle of oven until golden, 20-25 minutes.
7. Immediately invert a rack over pan and flip focaccia onto rack, then turn right side up. Serve warm or at room temperature.