Fry the onion, garlic and mushrooms in a little olive oil. Do not fry them long enough to change their colour. Add the wine and simmer for about 5 minutes until the wine has largely soaked in. Crumble in the stock cube. Add the cream. Reduce the heat to slowly bring to the boil and leave to simmer and thicken- this should take 5-10 minutes. If it does not thicken enough, add a little more chicken stock cube and simmer a bit longer.