Place dough on a floured surface and dust very lightly with flour. Pat the dough into an 8-inch square. Work the dough as little as possible adding flour as necessary. The dough should feel soft and smooth all over, but not sticky.
Pour 1 tablespoon of the olive oil into a baking pan and brush the bottom and sides with the oil. Transfer the dough to the baking pan and pat to fit.
In a small bowl make a slurry with remaining olive oil and 1 tablespoon of water. Brush the slurry over the dough then sprinkle with fresh rosemary. Cover with a tea towel and let proof at room temperature for 40 minutes.
About 30 minutes before baking, place a broiler pan on the lower shelf and the baking stone on the middle shelf of the oven. Preheat to 450°F.
Using the handle of a wooden spoon, dimple the flatbread at 2-inch intervals. Place the focaccia on the hot stone. Pour the hot water into the broiler pan.
Bake for 25 to 27 minutes or until the crust is lightly browned. Remove from pan and transfer to a wire rack to cool.