2 medium leeks (white and pale green parts only), quartered lengthwise, then finely chopped
1/2 teaspoon salt
2 teaspoons unsalted butter
1 1/2 lb yellow-fleshed potatoes such as Yukon Gold
1 medium fennel bulb (sometimes called anise; 1 1/4 lb), stalks trimmed flush with bulb, bulb halved lengthwise and thinly sliced crosswise)
1/3 cup low-sodium fat-free chicken broth
2/3 cup 1% milk, heated
1/2 teaspoon black pepper
Special equipment: a potato ricer, or a food mill fitted with medium disk
Directions
Wash leeks in a bowl of water, then lift into a sieve to drain.
Cook leeks with 1/4 teaspoon salt in 1 teaspoon butter in a 10-inch nonstick skillet over moderately low heat, stirring occasionally, until soft and beginning to brown, 6 to 8 minutes, then transfer to a bowl. Reserve skillet.
Peel and quarter potatoes, then cover with salted cold water by 1 inch in a 4-quart saucepan and simmer until tender, 20 to 25 minutes.
While potatoes are simmering, cook fennel with remaining 1/4 teaspoon salt in remaining teaspoon butter in skillet over moderate heat, stirring occasionally, until softened, about 5 minutes. Add broth and simmer, covered, until tender, 10 to 12 minutes.
Drain potatoes and force through ricer or food mill back into saucepan. Stir in milk, leeks, fennel, and pepper.
