Peruvian Potatoes with Spicy Cream Sauce ~ Papa a la Huancaina

4 medium Russett potatoes
8 ounces feta cheese, crumbled (about 2 cups)
1/3 cup evaporated milk
1/2 cup vegetable oil
1 tablespoon seeded and finely chopped jarred aji amarillo peppers or fresh habanero
1 garlic clove, finely minced
1/2 lime, juiced
Salt
4 large lettuce leaves (such as Bibb or romaine)
3 hard-boiled eggs, peeled and sliced
10 black olives pitted and sliced (Kalamata or Botija Peruvian olives)
2 tablespoons freshly chopped flat-leaf parsley