Preheat grill to medium.

Boil a gallon of water in a large pot. Add potatoes and boil 5 minutes. Remove with slotted spoon; cool until easy to handle.

Slice potatoes lengthwise into 1/2"-thick planks. In a large bowl, toss with olive oil, salt, and pepper (save the oily bowl to smash them in later). Grill potatoes on both sides until golden brown, 10–15 minutes. When done, they will appear dry and break in half easily when split with tongs. Transfer potatoes to bowl.

Smash potatoes roughly with a spoon. Gradually stir in warm milk.

Add chives and season.

Drizzle olive oil over the top of each serving.

	Smash potatoes roughly with a wooden spoon. Stir in the warm milk slowly.