My mom and aunt make the best mashed. This is their recipe with a little bit of my influence.
1/2-3/4 stick butter
Milk or cream
Salt to taste
Pepper to taste
Cut potatoes into fairly even sized pieces. Combine potatoes and enough cold water to cover the potatoes by about 2 inches. Boil potatoes until very tender. Drain in a colander and transfer to a mixing bowl. add butter and a little milk or cream. Mix with an electric mixer or hand masher. Add salt and pepper to taste. Add milk in small amounts until you reach your desired consistency. Cover with foil or plastic wrap and place near the oven vent on your stove top to keep warm.