South African Potato Salad with Condensed Milk

Name: South African Potato Salad with Condensed Milk
Ingredients: 2 kilogram (4lb) raw potatoes; 3-4 large shallots, or 1 medium onion, finely diced (roughly 120g/4oz chopped); 4 hard-boiled eggs, peeled and finely chopped (optional); ½ cup fresh parsley, finely chopped; 1 cup full-fat mayonnaise (good quality); ½ cup sweetened condensed milk; ½ cup sour cream; 1 tablespoon Dijon mustard; 2 tablespoons lemon juice (roughly half a large lemon); 2 teaspoons salt (or to taste); 1 teaspoon coarse black pepper (or to taste)