This may be hard to believe when every sandwich shop and supermarket in the land now seems to offer "focaccia" alongside white, wheat, and rye, but when I started going to Italy in the 1960s, this simple flatbread was virtually unknown in America, at least outside hardcore Italian neighborhoods.
There are different versions of focaccia all over Italy, but this is the crisp, if admittedly oily, variation preferred in Liguria.
Oil a large bowl and set it aside. Pour the water into a medium-sized bowl, dissolve the yeast in the water, and let stand until foamy, about 5 minutes. Stir in the oil.
Mix together the flour and 1 teaspoon salt in a large bowl, and make a well in the center. Pour the yeast mixture into the well, then stir the yeast mixture into the flour with a wooden spoon until a slightly sticky dough forms. Add a little more water if necessary to achieve the correct consistency.
Turn the dough out onto a floured work surface. Coat your hands with flour, then knead the dough until it is smooth and elastic, 2-3 minutes. Shape the dough into a ball, put it into the oiled bowl, and roll it in the bowl to coat it lightly with oil on all sides. Cover the bowl with a kitchen towel and set it in a warm spot until the dough roughly doubles in size, about 2 hours.
Lightly oil a 7-by-11-inch baking pan. Turn the dough out onto a floured work surface and shape it into a rectangle to fit the baking pan. Put it in the oiled pan and pat the top down gently so it is even. Using the handle end of a wooden spoon, make regular rows of slight indentations across the entire surface, spacing the indentations about 2 inches apart. Cover the pan with a kitchen towel and allow the dough to rise for another hour at room temperature.
Preheat the oven to 450 degrees.
Brush the top of the dough lightly with oil, then sprinkle with salt. Bake until golden brown, 20-25 minutes. (If desired, sprinkle 2 tablespoons rosemary or thyme leaves over the top of the focaccia after it has been in the oven for about 10 minutes.)
Serve warm or at room temperature, cut into wedges or squares.