Cut the mushrooms into slices. Finely chop the onions and garlic.
Let the pan get hot, brush with 1 teaspoon of olive oil. Add the mushrooms and sauté them. Immediately add the onions and garlic (don`t worry, they won`t burn). All of this has to be done at a relatively high heat so that the mushrooms brown quickly and do not start to cook. As soon as the mushrooms are the desired color, season with salt and pepper. Deglaze immediately with as much stock as you want the sauce. Let the whole thing simmer for about 15 minutes. Pour in the low-calorie cream, reduce the temperature significantly. Now season with a pinch of cayenne pepper, a pinch of sugar and a few drops of Worcester sauce. Stew on the lowest heat for another 10 minutes. If the sauce is too thin, you can sprinkle some locust bean gum into it. When the sauce has the desired consistency, add a little grainy mustard to taste. Add the chopped parsley.
Season the schnitzel with salt and pepper and fry in 1 teaspoon of olive oil. Serve the schnitzel with the sauce.