2 pounds Russet or Idaho potatoes
2 teaspoons salt
4 tablespoons unsalted butter
1/3 cup mayonnaise
1/3 cup milk
salt
pepper
Wash, peel, and cut the potatoes into 1-inch cubes. (You'll want them to be as close in size as possible so they cook evenly.) Place the potatoes into a large pot and just cover with water. Add 2 teaspoons of salt and bring to a boil. Reduce the heat to a low boil, stirring occasionally, and cook for 15 to 20 minutes or until the potatoes are tender when pierced with a fork.
Drain the potatoes and return them to the pot. Add the butter, mayonnaise, and milk. Use a potato masher to mash the potatoes to your liking. (You can also use a hand mixer to mash the poatotes, just be cautious not to over mix or they may become paste-like.) Mix well. Add more milk if necessary to get them to a smooth consistency. Add salt and pepper to taste. Serve with melted butter on top, if desired.