Golden Mashed Potatoes with Leeks and Sour Cream

INGREDIENTS

• 4 lb. large Yukon Gold potatoes, unpeeled
• and preferably organic, scrubbed
• 8 Tbs. (1 stick) unsalted butter
• 4 leeks, white and light green portions,
• finely chopped and rinsed well
• 1 cup sour cream, at room temperature
• 1 cup milk, heated to a simmer
• 1⁄2 tsp. salt, plus more, to taste
• 1 tsp. freshly ground pepper, plus more, to taste