2 tablespoons extra virgin olive oil
4 large leeks, thinly sliced (use only the light green portions)
5 cups low-sodium vegetable broth
1 large russet potato, peeled and diced
2 teaspoons chopped fresh tarragon
1 cup low-fat plain Greek yogurt
1 teaspoon salt
Freshly ground black pepper
1∕4 cup minced chives, for garnish
1. Over low heat in a large saucepan, heat the olive oil until shimmering. Add the leeks and cook, stirring often until just soft but not mushy, about 10 minutes. Pour in the broth, add diced potatoes, increase heat to medium and bring to a boil. Reduce to a simmer, cover and cook about 20 minutes more, until potatoes are tender.
2. Add fresh tarragon, stir, then purée (working in small batches) in a food processor or blender (after puréeing, open food processor or blender slowly to avoid splattering), then return puréed soup to a saucepan over low heat.
3. Stir in Greek yogurt (do not bring back to a simmer or the yogurt may curdle). Season with salt and freshly ground pepper to taste and serve garnished with minced chives.