Peel the potatoes and cut them into ½-inch / 1. 25 cm dice.
Boil them in salted water until they are just fork-tender, then drain completely and allow to cool slightly.
In a high-speed blender, combine 2 cups / 475 ml of the buttermilk, half of the cooked potatoes, half of the chopped green onions, the dill, and the minced garlic.
Blend at high speed until the mixture is completely smooth and puréed.
Pour the purée into a large bowl or tureen.
Stir in the remaining buttermilk, the rest of the diced potatoes, the remaining green onions, the chopped cucumber, cilantro, salt, and cumin.
Mix well to combine.
Cover and chill in the refrigerator for at least 2 hours, or until thoroughly cold, before serving.
Garnish with a swirl of good-quality olive oil, a few extra sprigs of fresh dill, and some freshly cracked black pepper just before serving to elevate the presentation and taste.
