Peel the potatoes and chop them into large chunks. Do the same with the turnips, cutting them into large chunks.
Take russet potatoes, skinned and large chopped, put in 2 turnips, skinned and large chopped. Boil in the water or chicken broth until the vegatables are soft and then process with a hand mixer in the pot to soup consistency (or transfer in batches to a blender).
Add the shredded carrots and 1 stick of butter. Cook on low heat until the carrots are soft and all flavors are melded. Season to taste with salt and pepper.