Potatoes with Cheese Sauce (Papas a la Huancaí)

Cover potatoes with water in a medium pot and season well with salt, then briskly simmer, covered, until just cooked through, about 20 minutes. Drain and cool, then peel.

Meanwhile, mince and mash garlic to a paste with a pinch of salt, then blend with remaining ingredients in a blender until very smooth and thicker than heavy cream (if necessary, thin with milk). Season with salt.

Cut potatoes crosswise into ¼-inch-thick slices.

Spoon some sauce onto 8 small plates, then top with sliced potatoes. Serve remaining sauce on the side.