Melt the butter in a large frying pan and fry the onions until softened. Stir in the mushrooms and cook for 2 minutes.
Add the flour and cook for 1 minute, stirring. Blend in the stock, Schwartz for Chef Black Pepper, Herbes de Provence, Mustard and Salt. Stir in the soured cream and sweetcorn and simmer for a further 2-3 minutes or until heated through.
