2 tbsp (30 g) unsalted butter 1 tbsp (15 ml) olive oil 2 large leeks (white and light green parts), thinly sliced and well rinsed 1 small Yukon Gold potato, peeled and diced (3 oz / 85 g) 1 small celery stalk, sliced 1 garlic clove, thinly sliced 1 / 2 cup (120 ml) dry white wine 4 cups (960 ml) low-sodium chicken or vegetable stock 2 fresh thyme sprigs 1 bay leaf 4 cups (about 2 small bunches) loosely packed watercress, thick stems removed 1 tsp finely grated lemon zest 1–2 tbsp fresh lemon juice, to taste 2 tbsp (30 ml) crème fraîche or plain Greek yogurt Kosher salt and white pepper, to taste Chive oil: 1 / 4 cup (60 ml) extra-virgin olive oil 2 tbsp (8 g) chopped fresh chives Pinch of salt
Make chive oil: Blend or finely chop chives with olive oil and a pinch of salt until vivid green; let sit while you make the soup (strain if you prefer a clear oil). In a pot, warm butter and olive oil over medium heat. Add leeks, celery, and a pinch of salt; cook gently until soft and translucent, 6–8 minutes. Add garlic and cook 30 seconds. Stir in potato, then pour in white wine; simmer 2–3 minutes to reduce by half. Add stock, thyme, and bay leaf. Bring to a gentle simmer and cook until potatoes are tender, 12–15 minutes. Remove thyme and bay. Add watercress and cook just until wilted, 45–60 seconds. Off the heat, blend until silky-smooth (use an immersion blender or carefully in batches). Stir in lemon zest, 1 tbsp lemon juice, and crème fraîche/yogurt. Season with salt and white pepper; add more lemon juice to brighten as needed. Rewarm gently if needed. Ladle into warm bowls and finish with a drizzle of chive oil. Serve immediately.
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