8 ounces leek – white and light green parts only, thinly sliced
3 tbsp unsalted butter
3 tbsp all-purpose flour
4 cups vegetable broth
0.5 cup heavy cream
1.25 tsp kosher salt
0.25 tsp ground white pepper
chives – finely snipped (for serving)
Instructions
Trim the asparagus by snapping off woody ends. Reserve the tips (about 1 inch) for garnish and cut the stalks into 1-inch pieces.
Rinse the sliced leek thoroughly in a bowl of water to remove grit, then drain well.
Melt the unsalted butter in a medium pot over medium heat. Add the leek and cook, stirring, until tender without browning, 6–8 minutes.
Stir in the all-purpose flour and cook, stirring constantly, until a blond roux forms, about 2 minutes.
Add the asparagus stalks and the vegetable broth. Bring to a simmer, then cook until the stalks are very tender, 10–15 minutes.
Add the reserved asparagus tips and simmer until just tender, 2–3 minutes. Using a slotted spoon, lift out the tips and set aside for garnish.
Off the heat, purée the soup until very smooth with an immersion blender (or in batches in a blender). For extra silkiness, pass through a fine-mesh sieve back into the pot.
Return the pot to low heat. Stir in the heavy cream, kosher salt, and ground white pepper. Warm gently without boiling, 3–5 minutes; taste and adjust seasoning.
Ladle into warm bowls and garnish with the reserved asparagus tips and chives. Serve immediately.