Stir the yeast into the warm water in a large mixing bowl. Let stand until creamy, about 10 minutes. Stir in 2 1/4 cups plus 1 tablespoon water and the oil. Add two cups of the flour and the salt and whisk or stir until smooth. Stir in the remaining flour, 1 cup at a time, until the dough comes together. Knead on a floured surface until velvety and soft, about 8 to 10 minutes.
First rise. Place the dough in a lightly oiled bowl, cover tightly with plastic wrap, and let rise until doubled, about 1 1/2 hours.
Shaping and Second Rise. For round focacce, cut the dough into 3 equal pieces on a lightly floured surface. Shape each piece into a thick disk; roll out each disk to a 9- or 10-inch circle and place in the bottom of an oiled pie plate. For rectangular focacce, cut the dough in half and shape to fit 2 oiled 10x15-inch pans. Cover the dough with towels and let rise for 30 minutes.
Dimpling and Third Rise. Dimple the dough vigorously with your fingertips, leaving indentations that are as deep as 1/2 inch. The bakers of Genoa do this to trap the little pools of oil and salt that flavor the surface. Cover the tops with moist towels and let rise until doubled, about 2 hours.
Topping. Paint the tops with oil and sprinkle with salt, (or any topping of your choice) and when you place the focacce in the oven spray with water.
Baking. Heat the oven to 400 degrees. Use baking stones if you have them (turn the oven on 30 minutes before baking) and place the pans directly on the preheated stones. Bake 20 to 25 minutes, spraying with water 3 times in the first 10 minutes; immediately invert the focacce onto racks to cool so that the bottom crusts don't get soggy.
Makes enough dough for three 9- or 10-inch round focacce or two 10x15-inch thinner rectangular focacce