Mix the butter, tarragon, black pepper and salt together until you have a smooth mixture.
Lay a sheet of plastic wrap on a work surface and scoop the butter mixture on to the centre of it. Use the plastic to form the butter into a 2.5 centimeter log. Roll the log into the plastic and twist the ends. Set the butter in the fridge for a minimum of 30 minutes.
Slice into rounds and use to flavour, steak, baked potatoes or vegetables.