In a large skillet, with deep sides, heat the olive oil over medium heat. Add the onion and cook, stirring, until the onion begins to soften, about 5 minutes. Add the barley, stirring until all of the grains are evenly coated in olive oil. Cook, stirring frequently, for about 5 minutes. Add the wine and cook, stirring, until it is nearly all absorbed. Add 1 cup of the warm stock to the pan, and continue stirring, until the stock is nearly all absorbed. Continue cooking the barley this way, adding the stock a bit at a time and stirring frequently, until the barley is tender enough to eat but still has a slight chew, about 50 minutes. (Note: The finished risotto should be creamy but not soupy. I found that I needed to cook it for between 50 and 60 minutes, and used nearly all of the stock. If you run out of stock, simply keep adding water until the barley is cooked.) Add any of the optional add-ins and continue cooking for a couple minutes, just until the ingredients are heated through.