Pour the stock into a saucepan and bring to a simmer.
Heat the oil in large, deep frying pan and cook the onion for 5–8 minutes until tender. Add any chopped mushroom stems and cook to just soften. Add the barley to the pan and stir to coat, then add the wine and leave to bubble for 2–3 minutes. Stir in 2 ladles of the stock and cook, stirring, for 5 minutes. Keep adding stock, a few la