Peel the potatoes and swede. Cut into large chunks and cook in separate pans.
Place in cold water with salt and bring to the boil. When the water comes to the boil, reduce to a simmer and cook until the vegetables are completely cooked.
Strain into a colander and allow the steam to evaporate for a couple of minutes.
Mash the potatoes and swede separately and stir in the butter. Season with salt and freshly ground pepper and serve immediately.
«allowing the steam to evaporate before you mash the vegetables will ensure that the mash is not too liquid.»