Bring salted (1 teaspoon salt) water to a boil over medium heat, then add potatoes. Reduce the heat and simmer until the potatoes are very tender, about 20 to 25 minutes then drain. Add the lemon zest, half the milk and cream, and season with salt and pepper, to taste. Use a potato masher to break up the potatoes and add the milk and cream as you go along - to just 'wet' the potatoes. Add more, for desired creaminess. Spoon the potatoes into a serving bowl and serve immediately.