In a medium saucepot, cover potatoes with cold water, add a pinch of salt, and place on stove over medium heat. Bring potatoes to a boil and cook until fork tender (approximately 10 minutes, depending on the size of the potato pieces). Combine the milk and butter and warm until butter is melted.

When potatoes are tender, drain thoroughly. Mash potatoes until smooth with a masher or push through a ricer or food mill. Add warmed milk and butter mixture; stir until combined. Salt and pepper to taste.

Spread in even layer on tray and place in refrigerator until chilled (for use in the whitefish cake mixture).