1 medium leek, white and pale green parts only, halved lengthwise, then finely chopped
1/2 teaspoon kosher salt
2 teaspoons unsalted butter
1-1/2 pounds Yukon Gold potatoes, peeled and quartered
1/2 medium fennel bulb, halved lengthwise and thinly sliced crosswise
1/3 cup gf
Chicken Stock2/3 cup milk, heated
Salt and freshly ground black pepper to taste