½ tsp. freshly ground black pepper
1 - ½ tbsp. kosher salt
1 tbsp. chopped fresh rosemary
4 tbsp. unsalted butter, softened
½ - ¾ cup milk
½ cup plain Greek yogurt or sour cream (I used non fat Greek yogurt)
1 cup cheddar cheese, divided
(6) garlic cloves, smashed and peeled
3 lbs. yukon gold potatoes, peeled and cut into about 1" cubes