These are one of my families favorite side dishes and they're so easy to make! Just simmer potatoes until tender, mashed well then beat with butter, cream, milk and sour cream. These are heavenly!
Peel, rinse and dice potatoes into large chunks (I diced my medium potatoes into 6 pieces total). Fill an 8 quart saucepan with 3 cups cold water (pan should have about 1/2-inch of water).
Add diced potatoes to cold water. Heat potatoes over high heat, stirring occasionally, until water begins to boil. As soon as water begins to boil, reduce heat to medium high and cover pan with lid and cook about 20 - 25 minutes, stirring once halfway through cooking and keeping a close eye on the water level* until potatoes are very tender when pierced with a fork.
During the last few minutes of cooking potatoes, heat heavy cream, milk and sour cream in a small saucepan over medium high heat until very warm, whisking occasionally.
Remove cooked potatoes from heat and strain any excess water from potatoes. Pour strained potatoes into a large mixing bowl. Pour melted butter over potatoes and mash potatoes with a potato masher until smooth, about 2 - 3 minutes (I wouldn't recommend using a wire type potato masher).
Pour 3/4 of the very warm cream mixture over mashed potatoes, season with 1 tsp salt and pepper to taste then using and electric hand mixer on low speed blend until well combine (adding more salt as desired).
Then increase speed to medium-high speed and whip for a minute or two, adding remaining cream mixture as desired to reach desired consistency (if you like thick mashed potatoes you may not want to add it, and if you like them thin you can add a little more milk to thin as desired), until potatoes are fluffy and smooth. Serve warm topped with gravy or butter if desired.
Notes
*3 cups works for me, but if your pan doesn't have a fairly tight fitting lid then a lot of water may evaporate and escape so you may need to add about 1/2 cup more hot tap water to prevent potatoes from burning.