Add 1-1/2 tablespoons olive oil, then immediately add 1/3 cup batter to the pan, swirling it around to evenly coat the bottom. Top with 1/4 of the caramelized onions and the 1/4 herbs and broil about 8 inches below the heat until lightly browned, 3 to 4 minutes. Transfer to a platter or cutting board, slice into wedges, season with salt, and serve immediately.