Put the potatoes in a large pot and add enough cold water to cover by several inches. Season the water liberally with salt. Bring to a simmer and cook until the potatoes are tender, about 15 minutes.
Drain the potatoes well and return to the pot with the butter, milk and sour cream. Season with 1 1/2 teaspoons salt and some pepper. Mash with a potato masher until slightly chunky. Crumble the pot-pie filling into the potatoes and mash until incorporated but not mushy. Fold in the parsley. Serve hot.