Place chopped potatoes in a pan and pour vegetable broth over to cover. If it doesn't cover completely, add enough water to do so. Bring to a boil, then cover and simmer for 10-15 minues or until tender.
Drain potatoes, return them to the pan, add the butter and mash the potatoes with a fork.
Add milk and sour cream and stir to thoroughly combine. Season, if necessary, and serve.