Leftover Turkey Avgolemono

Name: Leftover Turkey Avgolemono
Ingredients: 4 cups turkey stock or low-sodium chicken broth; 3 medium leeks, white and light green parts cut into 1-inch rounds, well washed; 3/4 cup orzo; Kosher salt and freshly ground black pepper; 2 large egg yolks; 3 tablespoons fresh lemon juice; 2 cups shredded leftover turkey; 2 cups watercress, plus more for serving; Extra-virgin olive oil, for drizzling