Ingredients
1 large swede weighing at least 1kg 
1kg potaotes - I like Vivaldis 
25g butter 
2 tbsps cream (optional) 
Salt 
White pepper

Equipment 
Potato masher or ricer

Method
Peel the swede and cut into smallish chunks.  Put the swede into a large pan of water with a tbsp of salt and bring to the boil.  Once the water boils, reduce the heat to medium so your swede is cooking on a high simmer for 15 minutes.   

Meanwhile peel your potatoes and cut into chunks.  Once the 15 minutes cooking time for the swede is up, add the potatoes to the pan and cook for a further 20-25 minutes until a knife slides easily through. Drain through a colander. 

Put the vegetables back into the pan and over a medium heat just turn the potatoes for a min or so drying out any water that is in the bottom.  Thoroughly mash with a potato masher or ricer until the vegetables are as smooth as you can get.  Add the butter and white pepper and mash through.  Taste, adding the cream if you would like to and checking the seasoning.