Boil the Potatoes and Carrots: Start by peeling and cutting the potatoes and carrots into small, even pieces. Boil them in a pot of salted water until they are tender (usually around 15-20 minutes). Drain and let them cool.
Prepare the Eggs: While the potatoes and carrots are cooking, hard-boil the eggs. Once they are done, peel and chop them into small pieces.
Chop the Vegetables: Dice the cucumber into small cubes.
Mix the Dressing: In a mixing bowl, combine mayonnaise, sweetened condensed milk, sugar, salt, and pepper. Mix until smooth and creamy.
Combine Ingredients: In a large mixing bowl, gently combine the boiled potatoes, carrots, chopped eggs, and diced cucumber. Be careful not to mash the potatoes too much; you want some texture.
Add the Dressing: Pour the creamy dressing over the potato mixture and fold everything together until well coated.
Chill and Serve: Refrigerate the salad for at least an hour before serving to let the flavors meld. Garnish with a sprinkle of pepper before serving.