Wash the potatoes and place in a large pot (unpeeled). Cover with cold water and bring to the boil. Add a pinch of salt and cook, uncovered, until the potatoes are tender all the way through (approximately 30 minutes after the water has come to a boil). Drain the potatoes. Prepare a medium sized bowl to place the mashed potatoes.
While the potatoes are still hot, cut them in half and place cut side down into a potato ricer. Remove the potato skins each time you place a piece of potato into the potato ricer. Alternatively remove the potato skins while hot and mash using a tamis (drum sieve) into a bowl. Pass the mashed potatoes through the potato ricer or tamis a second time to achieve a smooth mash.
Transfer the mashed potatoes back to the pot. Place the milk in a small saucepan over low-medium heat and bring to the boil. Reduce the saucepan with milk to low heat and simmer. Place the pot with mashed potatoes on low heat. Stir in the milk until well combined, then add the cold butter. Season with sea salt to taste and stir until well combined.
4 large potatoes (unpeeled) such as Desiree (approximately 1 kg)|150g of unsalted butter|150ml of full cream milk|Sea Salt