vegetable stock and heat, stirring all the time until thickened. 3. Blend in the mustard and remove from the heat. 4. In another pan melt the remaining butter and add the mushrooms and onions and saute for 5 minutes until the onions start to soften. 5. Add the mushrooms to the sauce, and simmer for 15 minutes. Remove from the heat and stir in the sour cream. 6. Stir in the onions, and serve. I sometimes add coriander or lemon grass. Lemon grass goes down well, and if you add coconut milk/cream instead of the sour cream,lime juice and tomato paste you get a nice Thai mushroom dish. Thai dishes are often like a soup, so increase the liquid a bit and serve in a large bowl with two spoons so you can share it, and a large plate of rice. It's one of my own creations so report back!