Tomato and Parmesan Focaccia with Caramelized Onions

Serve this delicious snack warm or at room temperature. Although you can prepare it in a day, it is best done on the day of baking.
To make the dough, combine the first 4 ingredients in a large bowl, stirring to allow the yeast to dissolve; let stand for 5 minutes. Lightly pour the flour into dry measuring cups; smooth with a knife. Add 2 1/2 cups flour, cornmeal, and 1 teaspoon salt to the yeast mixture; mix well. Place the dough on a floured surface. Knead until smooth and elastic (about 10 minutes); add enough remaining flour, 1 tablespoon at a time, to keep the dough from sticking to your hands.Place the dough in a large bowl greased with cooking spray, turning it over so that it covers the top. Cover and let rise in a warm place (85 °), draughty, for 1 hour and 30 minutes, or until doubled in size. (Gently press two fingers into the dough. If there are dents, it means that the dough has risen sufficiently.)To make the topping, heat 1 tablespoon of oil in a large nonstick skillet over medium-high heat. Add the onion, dried basil, 1/2 teaspoon salt and pepper; cook for 20 minutes or until the onion is golden, stirring occasionally. Cool.Arrange the tomato slices between several layers of paper towels. Let stand for 10 minutes, pressing occasionally.Roll out the dough. Knead the dough; cover and let stand for 5 minutes. Place the dough in an even layer on a 15-inch x 10-inch jelly roll pan smeared with cooking spray. Cover and let rise for 30 minutes.Preheat the oven to 425 degrees.Roll out the dough. Spread the onion mixture on top of the dough, leaving a 1/2-inch thick rim. Top with tomato slices; sprinkle with cheese. Bake at 425 ° C for 23 minutes or until lightly browned. Sprinkle with fresh basil. Let cool for at least 10 minutes before serving.