In a large saucepan, sauté onions in hot oil until translucent. Add the porcinis and sauté on medium heat until lightly browned, 10 minutes. Add the wine and cook until the alcohol evaporates.
Add the chestnut purée and mix well; add the meat stock, season with salt and pepper, and cook for 20 minutes (without boiling).
Mix the cornstarch with the cream, add to the soup, and quickly bring to a boil. Serve with crusty bread.