• 6 medium leeks (about 2 1/2 pounds)
• 3 tablespoons extra-virgin olive oil, divided
• 1 tablespoon unsalted butter
• 1/2 teaspoon kosher salt and freshly ground black pepper
• 1 cup low-salt chicken stock
• 2 tablespoons chopped flat-leaf parsley, divided
• 1 tablespoon coarse-grained Dijon mustard
• 1 tablespoon white wine vinegar
• 2 hard-boiled eggs, whites and yolks separated and chopped