Cooked on a baking sheet and sliced into squares, flatbread makes a versatile alternative to your standard dinner rolls. And your kids can lend a hand by pressing the dough into the pan and drizzling it with olive oil. In this version, cornmeal gives the bread a crispy crust, the perfect base for layering on fresh tomato, rosemary, and Parmesan.
Measure the water into a large mixing bowl. Sprinkle the yeast over the water and stir it with a wooden spoon. Let the mixture stand until the yeast dissolves and small bubbles form, about 5 to 7 minutes.
Add 4 cups of the flour, the cornmeal, and the table salt and stir the mixture until the ingredients are uniformly combined. Stir in the olives, if you're using them. Add another 1/2 to 1 cup of flour and knead the dough in the bowl until it holds together.
Turn the dough out onto a floured surface and knead it until smooth and elastic, 5 to 7 minutes. Shape the dough into a ball.
Measure 1 tablespoon of the olive oil into a large bowl. Add the dough, then turn it to coat all sides. Cover the bowl with plastic wrap and let the dough rise in a warm area until it has doubled, generally 1 to 1-1/2 hours.
Heat the oven to 475ºF. Coat a rimmed baking sheet (ours was 17 by 12 inches) with 1 tablespoon of the olive oil. Punch down the dough and transfer it to the prepared sheet, using your fingertips to press it out to fit the pan.
Drizzle the remaining 2 tablespoons of oil over the dough. Again, let the dough rise in a warm area, uncovered this time, until it's puffy, about 30 minutes.
Press your fingertips into the dough to form small indentations across the entire surface. Then top it with the sliced tomatoes and red onion, and season it with the coarse salt and freshly ground pepper. Distribute the rosemary leaves across the surface, lightly pressing them into the dough.
Bake the bread until it's brown and crusty, 20 to 25 minutes, then top it with Parmesan. Enjoy it warm or at room temperature. Serves 8 to 10.