Heat the broiler with the rack 8 inches from the heat source. Stir together the flour, 2 cups water, the oil, and 1 tablespoon salt in a medium bowl.
Oil a 12-inch cast-iron skillet; pour in the batter. Broil until golden brown, 3 to 4 minutes. Reduce oven to 400°F; bake until set, about 6 minutes. Sprinkle with the rosemary; season with salt and pepper. Cut into 8 wedges, and serve.
