1) Put the potatoes in a large saucepan with the cream and milk. Bring to a boil over medium heat, then add 1 tsp of salt. Reduce the heat and simmer until the potatoes are very tender, about 20 to 25 minutes. Remove about 480ml of the liquid and reserve. Add the lemon zest and season with salt and pepper, to taste. Use a potato masher to break up the potatoes while adding about 240ml of the reserved liquid, to just 'wet' the potatoes. Add more, for desired creaminess. Spoon the potatoes into a serving bowl and serve immediately.