Place beets and potato in large pot and bring to a boil to soften. When you can pierce beets and potato with a fork, they are done. Drain the water from the pot. If you like mashed vegetables with the skin on, you can simply begin to mash with your mixer or food processor. If you prefer the skin off, boiling the vegetables will make it a lot easier to remove the skin with a peeler, then mash together with the butter, salt and pepper, serve and enjoy!