Place potatoes and lemon juice in a large saucepan, and add enough water to cover. Bring to a boil over medium-high heat, and cook until tender, about 15 minutes.
Drain water from potatoes, and use a potato masher to mash. Stir in egg white and butter, and gradually mix in the half-and-half using the masher. Use more or less cream to reach your desired consistency. Season with salt and pepper to taste.