Traditionally served over broiled steak.
In a small bowl, cream with a fork or wooden spoon:
      4 tablespoons unsalted butter (preferably unsalted), softened
Gradually stir in:
      1 tablespoon finely chopped parsley
      3/4 to 1 1/2 tablespoons fresh lemon juice
      Salt and ground white pepper to taste
Roll the mixture into a cylinder in a piece of wax or parchment paper, plastic wrap, or aluminum foil (or shape as desired), and refrigerate or freeze until firm enough to slice. Or refrigerate in a small bowl or ramekin and spoon on just before serving.