- Cut the green part of the leeks. Set aside for another use (soup, broth, etc.). Wash the remaining white part of the leeks.
- In a vegetable steamer, steam the leeks until tender, about 10 minutes. Let cool, then refrigerate.
- In a bowl, whisk together the egg yolk and vinegar. Whisk in a little oil. Add the remaining oil in a thin stream while whisking. Season with salt and pepper.
- Drizzle the cold leeks with the vinaigrette.