- Combine mushrooms and butter in large pan, and place over medium heat. Season lightly with a pinch of salt and black pepper.
- Cook mushrooms stirring occasionally until they release all their water and seem to be boiling.
- Allow mushrooms to continue cooking until all liquid is cooked off and pan is nearly dry, again stirring occasionally.
- Once pan is nearly dry keep cooking mushrooms over heat stirring more and more frequently until they are all uniformly caramelized to deep golden brown.
- Remove pan from heat and add apple cider vinegar, stir well to incorporate evenly. Adjust seasoning with more salt and black pepper as needed.
- Pour mushrooms in large bowl and garnish them with preserved lemon and chervil.