Add the chopped potatoes to a large saucepan and cover with cold water.
Keep adding the cold water to the pan until the potatoes are covered by at least an inch.
Then add a half teaspoon of salt to the water.
Bring the pan to the boil, then reduce to a medium simmer and half cover with a lid.
Cook until the potatoes are tender for approximately 20 minutes; drain the potatoes in a colander and return them to the saucepan.
In a separate saucepan, heat the milk.
Using a potato masher, mash the potatoes until they are smooth.
Add the butter and the milk to the potatoes and stir vigorously.
Stir in the cheese and keep stirring until the cheese has been incorporated.
Then season with salt and black pepper.
Although this step is completely optional, garnishing with spring onion and parsley will give a burst of flavor.