Instructions

• Trim and prepare the leeks: cut off the root ends and discard the dark green, tough tops so you are using only the white parts. Slice the white parts lengthwise, rinse thoroughly between layers to remove any grit, then dice to make about 6 cups.
• Prepare the potatoes: peel the Yukon golds and cut into 1-inch dice (about 3 cups). Place the diced potatoes in a bowl, cover with cold water, and set aside to prevent browning.
• In a large pot over medium heat, melt most of the 4 tablespoons of butter, reserving the remainder for finishing the soup.
• Add the diced leeks to the pot and cook, stirring occasionally, until soft and fragrant but not browned, about 15 minutes.
• Sprinkle the 2 tablespoons of all-purpose flour over the cooked leeks and stir to coat. Cook and stir for 1 to 2 minutes to remove the raw flour taste.
• Drain the potatoes and add them to the pot. Pour in 2 cups chicken (or vegetable) broth, 2 cups half-and-half (or whole milk), and add the bay leaf. Whisk to combine.
• Bring the mixture to a gentle boil, then reduce the heat to medium-low and simmer uncovered until the potatoes are easily pierced with a fork, about 15–20 minutes.
• Remove the pot from the heat. Discard the bay leaf. Stir in 1 teaspoon kosher salt and 1/2 teaspoon freshly ground black pepper. Let the soup stand about 5 minutes to cool slightly.
• Purée the soup until smooth: either use an immersion blender directly in the pot, or transfer the soup in batches to a blender. If using a blender, remove the center piece of the lid to allow steam to escape and cover the lid opening with a towel to prevent splatters. If you prefer a chunkier soup, reserve about 2 cups of the soup before puréeing and add it back after blending.
• Return the puréed soup to the pot, stir in the reserved butter, and warm over medium-low heat—do not boil. If the soup is too thick, thin with additional half-and-half or whole milk a little at a time until you reach the desired consistency. Taste and adjust seasoning with more salt if needed.
• Serve hot, topped with freshly ground black pepper and minced fresh chives.