2 1/2 pounds Yukon Gold potatoes (5 to 6 medium), peeled and chopped
2 sticks salted butter, cut into pieces, at room temperature
2 leeks (white and light green parts), thinly sliced and rinsed
1 teaspoon chopped fresh thyme
1 teaspoon chopped fresh rosemary
Freshly ground pepper
1/2 to 3/4 cup milk, warmed
For plain mashed potatoes, follow the recipe for Mashed Potatoes with Leeks, but skip Step 2.