Directions

1. Heat oil and butter in a large, heavy saucepan over low heat. Add leeks and stir well. Cover and cook until soft, about 5 minutes.
2. Add stock and bring to a simmer over medium-high heat. Add salt and pepper to taste. Add potatoes and bring back to a simmer. Cook until tender but not mushy, 10 to 15 minutes. Turn off heat.
3. Ladle about 3 cups of soup into a blender (don't fill more than half full). Hold the lid on with a dish towel to prevent splattering, and blend until smooth. Return pureed soup to saucepan, stir to combine, and bring back to a simmer. Season to taste.
4. Stir in greens. Cook for 2 to 3 minutes, until wilted and bright green, and serve immediately.