Whip or beat the butter with parsley together in a bowl and season with salt and pepper. Spoon into a large piece of parchment paper or plastic wrap, roll it into a log, and seal the ends. Alternatively, you can simply smoosh the butter into a ramekin or other small dish, leveling the surface with a knife.
Refrigerate until firm, about 1 hour. Keep your stash of parsley butter in the fridge for up to 1 month or freeze for up to 3 months. To prevent icky aromas from infiltrating your butter, wrap the parchment paper (or ramekin) tightly with plastic wrap or aluminum foil. Slice or set out on your dinner table while the butter is still cold.