Ingredients:

  • Unsalted butter: 2 tbsp (28 g) OR olive oil 2 tbsp (30 ml) for dairy-free
  • Leeks (white and light green only): 3 large, trimmed, halved lengthwise and thinly sliced — about 12–14 oz (350–400 g) after trimming
  • Medium yellow onion (optional): 1 small, finely chopped (~100 g)
  • Garlic (optional): 1–2 cloves, minced
  • Yukon Gold or Russet potatoes: 2 lb (900 g), peeled and cut into 1-inch (2.5 cm) cubes
  • Kosher salt: 1 tsp (6 g), plus more to taste
  • Freshly ground black pepper: 1/2 tsp, plus more to taste
  • Fresh thyme (optional): 1–2 sprigs OR 1/2 tsp dried thyme
  • Bay leaf (optional): 1
  • Low-sodium chicken stock or vegetable stock: 6 cups (1.4 L)
  • Whole milk or half-and-half (optional to thin): 1/2 cup (120 ml)
  • Heavy cream or crème fraîche (optional finish): 1/2 cup (120 ml)
  • Fresh chives, chopped, for garnish: 1–2 tbsp
  • Optional toppings: crispy bacon or pancetta, chopped (4 slices); extra crème fraîche or plain yogurt (1–2 tbsp per bowl); extra-virgin olive oil or chive oil drizzle

Instructions:

  1. Prepare leeks and aromatics: Trim root end and tough dark green tops; halve lengthwise and rinse between layers to remove grit, then slice thin. Chop onion (if using) and mince garlic.
  2. Sweat the leeks and aromatics: Melt butter or heat oil in a large heavy-bottomed pot over medium-low heat. Add leeks and onion (if using) with a pinch of salt and cook gently until soft and translucent, about 8–10 minutes. Do not brown.
  3. Add potatoes, herbs, and stock: Add potato cubes, thyme or dried thyme and bay leaf, then pour in enough stock to cover (about 6 cups). Bring to a simmer over medium heat.
  4. Simmer until tender: Reduce heat to medium-low and simmer uncovered until potatoes are very tender, about 15–20 minutes. Test that potatoes are fork-tender and breaking apart.
  5. Puré e the soup: Remove bay leaf and thyme sprigs. Use an immersion blender to purée to desired smoothness directly in the pot, or cool slightly and purée in batches in a countertop blender, venting steam carefully. For an ultra-smooth finish, pass the puréed soup through a fine-mesh sieve into a clean pot (optional).
  6. Finish and adjust: Stir in milk or half-and-half if needed to loosen texture, then add heavy cream or crème fraîche if using. Warm gently and do not boil after adding cream. Season to taste with salt and pepper and adjust thickness with more stock or milk as needed.
  7. Serve: Ladle into bowls and garnish with chopped chives, a spoonful of crème fraîche, and optional crispy bacon or pancetta or a drizzle of extra-virgin olive oil. Serve with crusty bread if desired.