Cut potatoes into ½ inch to 1 inch slices. Add them to a large pot.
Add cold water over the potatoes until they are all submerged into the water. Bring to a boil.
Cook for 25-30 minutes. Until they're fork tender.
Drain the potatoes from the water. Add them to the bowl of a stand mixer, or alternatively, add them to a large bowl. You can use a hand mixer, potato ricer, or mash them by hand if you don't have a stand mixer.
Add the butter to the potatoes and let it melt.
While it is melting, combine the sour cream and half and half.
Add half of the sour cream/half and half mixture, salt, and pepper to the potatoes.
Whip potatoes and add more of the sour cream/half and half mixture until they're your desired consistency.