Boil the potatoes in a large pot of salted water until tender, about 20-25 minutes. Drain and let cool.
Once cooled, peel the potatoes and slice them into rounds. Arrange the slices on a serving platter lined with lettuce leaves.
In a blender or food processor, combine the vegetable oil, aji amarillo paste, evaporated milk, crumbled queso fresco, minced garlic, lime juice, white vinegar, salt, and black pepper.
Blend until smooth and creamy. Adjust seasoning if needed.
Pour the Huancaína sauce generously over the sliced potatoes.
Garnish with sliced olives (if using) and hard-boiled egg slices.
Sprinkle with chopped fresh cilantro.
Enjoy your meal!