Peel and cut the potatoes into thick, relatively even slices.

To a large pot, add the potatoes, about 1 tbsp of salt, and cover with cold water (about 1-2 inches over). Bring to a boil over medium-high heat (about 10 minutes), and then simmer the potatoes for about 15 minutes until tender. It took me 25 minutes total time (using Maris Piper potatoes cut into relatively large pieces). You can check if the potatoes are fully cooked by inserting a pairing knife through the middle and if it goes in easily and slides out
easily, it’s done!

While the potatoes are boiling, wash and finely chop the scallions.

Also, while the potatoes are boiling, warm up the milk and 4 tbsp of butter (over the stove, over low heat, takes about 3-4 minutes). You can also warm up the milk and butter in the microwave in 30-second increments.

Drain the potatoes and mash them with a potato masher.

Add the hot milk-butter mixture a bit at a time while mashing with the potato masher.

Taste and adjust the seasoning, adding salt (to taste).

Add the chopped scallions.

Serve with more butter (about 2 tbsp) on top.