Carefully rinse the mushrooms and dry them with paper towels. Trim away any hard stem and slice finely or cut into small chunks.
Heat the olive oil in a saucepan and add the onion. Sauté on a low heat until it is very soft. Add the wine and when it has evaporated add the mushrooms and the sage, and sauté for a few minutes to colour them lightly. Add the hot stock and simmer for about 25