Prepare potatoes by cleaning and peeling them. Cut into 1-1/2" chunks. Place potato chunks into 5 qt pot filled with cold water. Give enough space at the top of the pot to allow for boiling without overflow.
Bring to a boil over high heat. When the water begins to boil, add 3 Tbsp of kosher salt and reduce heat to medium high. Take care to not allow the water to overflow. Boil 10-12 minutes based on the size of your potatoes, stirring occasionally. Drain and place potatoes in a bowl.
Add butter, milk and salt. Beat on low speed with a hand mixer until all ingredients are combined. Turn mixer to high for 30 seconds or until potatoes reach the consistency that you prefer. Serve warm.
Starting the potatoes in cold water insures that the potatoes cook evenly.