Cut the leek into slices. Sauté in olive oil in a small saucepan for 2 minutes. Peel the potatoes and cut them into slices.
Shape 4 pieces of aluminum foil into circles (approx. 16 cm each) and grease with butter. Arrange the potatoes in a circle. Place the leek slices on top and season everything with salt and pepper. Spread the raclette cheese on the potatoes.
Shape 4 more pieces of aluminum foil into circles, grease and place on the potatoes. Close tightly at the edges. Heat in a preheated oven at 180 ° C for about 30 minutes. Do not turn.