Put peeled, cubed potatoes into a medium size pot and cover with cold water. Bring the potatoes to boil over medium high heat and let cook about 30 minutes or until fork tender. Drain the potatoes, do not rinse. Put the stick of butter into the hot dry pot and dump the potatoes on top. Mash the potatoes and butter together with a hand masher just until broken up and the butter begins to melt into the potatoes. Add the whipping cream and beat with a electric mixer until there are no lumps and the potatoes are light and fluffy. Add or reduce the amount of whipping cream to make the potatoes the consistency that you like. Add salt and pepper to taste.