Using a brush and a damp sponge, clean the mushrooms; trim and slice the mushrooms lengthwise.
In a large frying pan over medium-high heat, melt 2 tablespoon butter; add mushrooms and saute for 5 minutes, stirring frequently. Sprinkle parsley over the mushrooms and season with salt and pepper. Reduce heat to low.
In a separate saucepan, melt the remaining 1 tablespoon butter; stir in flour, egg yolk, and lemon juice until combined. Pour the lemon sauce over the cooked mushrooms and stir over low heat (do not let boil) for a couple of minutes until the sauce thickens. Remove from heat and serve immediately.
Makes 6 servings.
* You could use any type of mushroom that you prefer.
Mushrooms in Lemon Sauce Recipe - Fricassea di Funghi: https://whatscookingamerica.net/Vegetables/MushroomsLemonSauce.htm