Place the halved potatoes in a large pot, cover them with salted water, and bring to a boil.

Reduce the heat to medium-low and simmer until tender, about 20 minutes.

Drain the potatoes well, return them to the pot, cover with a clean dish towel, and place over very low heat for 2-3 minutes to dry.

While the potatoes are drying, heat the milk and sliced green onions in a saucepan over medium-low heat until warm, about 3-4 minutes.

Once the potatoes are dry, add the butter and salt, then mash with a potato masher until smooth.

Stir in the warm milk and green onion mixture until well combined, then season with freshly ground black pepper to taste.