Use a large pot and add 4 litres of water over high heat and add 1 tbsp of salt. Bring to a boil and add the potatoes. Once it comes to a boil again cook them for about 25’ until soft (check with a fork).
In the meantime, Put the milk in a small saucepan on medium heat and once it boils take it off the heat.
Take the potatoes out of the water and let them sit for 10’. Then mash them with a potato masher while seasoning them with the 1 tsp of salt. Use a strong large whisk and stir in half the milk.
Whisk in the butter in small batches making sure that you add the next batch when the previous was incorporated and add the remaining milk to create smooth mashed potatoes. Finally serve in a bowl and sprinkle with the nutmeg.