Modern Shepherds Pie

Name: Modern Shepherd's Pie
Ingredients: 2 tablespoons extra-virgin olive oil; 6 ounces (1) leek, trimmed, rinsed and finely chopped; 4 ounces (2 medium) carrots, peeled and chopped; 4 ounces (100 grams) green beans, trimmed and chopped; 2 ounces (1 stalk) celery, finely chopped; 14 ounces (400 grams) canned red kidney beans, rinsed and drained; One 8-ounce (250-gram) pouch cooked black lentils, rinsed and drained; 1 teaspoon dried mixed herbs; 1/2 teaspoon chili flakes; 3 cups vegetable stock (made using 1 tablespoon bouillon powder); 2 tablespoons cornstarch, mixed with 2 tablespoons water; 1 tablespoon tamari (could use soy sauce); 1 tablespoon vegan Worcestershire sauce (no anchovies); 1 sprig of fresh rosemary; 2 1/2 pounds (1.2 kilograms) Yukon Gold or Maris Piper potatoes; Flaky sea salt; 1/4 cup plus 2 tablespoons extra-virgin olive oil; 1 tablespoon Dijon mustard; Freshly ground black pepper, to taste; 1/4 cup unsweetened plant-based milk; 1 small bunch parsley (about 2 tablespoons, finely chopped)