1. Wash the swede carefully and peel it.
2. Cut the flesh into square pieces
3. Put the swede into the saucepan with a few grains of salt and add just enough water to cover it.
4. Let in boil in moderate heat with the lid on. Once it has boiled, turn down the heat and let it bubbling very gently. This may take an hour or more.
5. Drain the Swede in the colander and put it in the saucepan again.
6. Add butter, salt and pepper and mash them altogether. You can also add Dijon mustard or Worcestershire sauce if you want.
7. Reheat over in a very low heat. Serve immediately.