1
In a large pan, add butter and onion and cook on medium heat for about 1.5 minutes or until onions softens.
2
Add mushroom slices, stir through mushrooms every minute until mushrooms and onion caramelised. Season with salt & pepper.
3
Reduce heat down to medium-low and stir in garlic for about 1 minute, until garlic is fragrant.
4
Deglaze the pan with stock, allow it to reduce by half. Reduce heat down to low and pour cream and dijon mustard in.
5
Mix cornstarch with some cold water well, pour into pan. Allow sauce to simmer and thicken lightly. Season again to taste.