Peel and chop the potatoes. Add to a pot and cover with water. Bring to a boil, cover, reduce heat to maintain a simmer. Continue cooking until fork tender, about 15 minutes.
Just before the potatoes are fully done, add the cauliflower rice, cover, and continue cooking until both vegetables are tender, about 5 minutes. Drain.
Add the cream cheese, butter, salt and pepper to the drained potatoes and cauliflower. Either mash by hand or process in stand mixer to mash up all of the lumps. Season with additional salt, if needed.
If using frozen cauliflower rice, be sure to fully thaw before adding to the boiling potatoes.