Boil the eggs until hard, then immediately transfer them to a bowl of cold water to chill.

Once cooled, peel the eggs carefully.

Cut the hard-boiled eggs crosswise and gently remove the yolks, being careful not to break the whites.

Set aside the egg whites.

In a bowl, mash the egg yolks with a fork, then add the butter, cooked chopped mushrooms, chopped parsley, salt, and pepper.

Mix well until the ingredients are fully combined and form a paste-like consistency.

Heat the yolk mixture in a saucepan over low heat, stirring constantly until warmed through.

Using a spoon or piping bag, stuff the egg whites with the warm yolk mixture, dividing it evenly among them.

Arrange the stuffed eggs on a serving platter, optionally over a bed of cress for presentation.

Serve the Stuffed Eggs with Mushroom and Parsley cold as an appetizer or side dish.