Cut and cover the potatoes: Peel the potatoes and cut them into even 1 1/2-inch chunks so they finish cooking at the same time. Put them in a large pot, add cold water until it covers them by an inch, and stir in the 1 tablespoon of salt.

Boil until tender: Bring the pot to a boil over high heat, then lower it to a steady simmer and cook uncovered for 15 to 20 minutes. They're done when a paring knife slides into a chunk and slips back off on its own with no resistance.

Drain and dry them out: Drain the potatoes well and return them to the empty hot pot. Let them sit over the turned-off burner for 2 minutes, giving the pot a shake once or twice. The leftover heat steams off surface water, and drier potatoes take on butter and milk far better.

Warm the milk: While the potatoes dry out, heat the milk in the microwave or a small saucepan until it's warm to the touch, about 45 seconds. Don't let it boil.

Mash in the butter first: Scatter the softened butter over the hot potatoes and mash with a potato masher or push them through a ricer until the butter disappears. Butter goes in before any liquid so it can coat the starch, which is what keeps the mash from turning sticky.

Add the milk to taste: Pour in about 3/4 cup of the warm milk and fold it in with a rubber spatula. Add the rest a splash at a time until the potatoes are as loose as you want them. Fold, don't beat.

Season and serve: Stir in the 1 1/4 teaspoons of salt and the black pepper, then taste and add more salt if they still seem flat. Potatoes take more salt than most people expect. Scatter the chives over the top and serve hot.