Preparation Whisk buttermilk, mayonnaise, lime juice, cumin, and cayenne in medium bowl to blend. Cook potatoes in large pot of boiling salted water until tender, about 20 minutes. Drain; cool. Cut potatoes into 1/2-inch cubes. Place potatoes in large bowl; add corn, onion, hearts of palm, tomatoes, and cilantro. Drizzle dressing over potato mixture; toss to coat. Season generously with salt. (Can be made 4 hours ahead. Cover and refrigerate.) Gently stir in avocado and serve. Test-kitchen tip: Pitting an avocadoCut an unpeeled avocado in half lengthwise. Grasp both sides and twist to open. Tap a large knife into the pit so it sticks, then twist the knife to loosen and remove the pit.
Preparation Whisk buttermilk, mayonnaise, lime juice, cumin, and cayenne in medium bowl to blend. Cook potatoes in large pot of boiling salted water until tender, about 20 minutes. Drain; cool. Cut potatoes into 1/2-inch cubes. Place potatoes in large bowl; add corn, onion, hearts of palm, tomatoes, and cilantro. Drizzle dressing over potato mixture; toss to coat. Season generously with salt. (Can be made 4 hours ahead. Cover and refrigerate.) Gently stir in avocado and serve. Test-kitchen tip: Pitting an avocadoCut an unpeeled avocado in half lengthwise. Grasp both sides and twist to open. Tap a large knife into the pit so it sticks, then twist the knife to loosen and remove the pit.