1 leek (white and pale green parts only), coarsely chopped
2 lb potatoes, preferably Yukon Gold or russet (baking) potatoes
4 carrots, cut into 1/2-inch chunks
2- to 3-inch cube of ginger
1/2 stick (1/4 cup) unsalted butter
3/4 cup whole milk
3/4 teaspoon salt
1/4 teaspoon black pepper
Wash chopped leek well in a bowl of cold water, then lift out and drain well.
Peel potatoes and cut into 2-inch pieces. Cover with cold water in a saucepan. Bring to a boil, then reduce heat and simmer, uncovered, until potatoes are tender, about 18 minutes.
Drain and return to saucepan. (see note below)