Peel cleaned potatoes and cut into approximately even, bite-sized pieces. Rinse potatoes through a strainer over your sink, and run through cold water for several seconds, removing the excess starch.
Fill a large pot with cold water and add a generous amount of kosher salt. Be sure to taste the water, as it should taste like 'salt water' but not too salty.
Add the potatoes. The water should come up just a little over the potatoes, so if you have too much water, pour out the excess. Bring to a rolling boil, stirring every so often.
You can check the doneness of your potatoes by sticking a sharp knife, like a paring knife, into a piece. If the knife goes in easily, the potatoes are done. The cooking process may vary, but plan anywhere from 20-30 minutes. Check potatoes any time after 20 minutes to gauge how far along they are, and at more frequent intervals from there. Overcooked potatoes will absorb too much of that salty water and will affect not only the taste but the texture as well.
Immediately drain the cooked potatoes into the sink over your strainer.
While the potatoes cool slightly, grab your mixer, ricer, and the remaining ingredients (butter, heavy cream and sour cream, salt and pepper)
Fill your ricer with warm potatoes and squeeze the riced potatoes directly into the mixing bowl. Repeat until all of the potatoes have been riced.
Add the diced butter to the riced potatoes and cream together until smooth.
Add sour cream and heavy cream, and blend.
Taste the potatoes and season accordingly with salt and pepper.
Keep potatoes warm until ready to serve.