Chives for garnish
1/4 tsp. freshly ground black pepper
2 tsp. kosher salt
1/4 tsp. fresh minced rosemary
1/2 cup plain or greek yogurt
8 oz. cream cheese
3 tbsp. unsalted butter
1 sprig fresh rosemary
3 cloves garlic, peeled and whole
5 pounds potatoes, peeled and cut into 2-inch chunks